Tag Archives: quantum mechanics

Can the future influence the past? The answer is: mostly yes

The principles of quantum mechanics mystify me which, as it turns out, is the perfect place to start with the work featured in a Feb. 9, 2015 news item on ScienceDaily,

We’re so used to murder mysteries that we don’t even notice how mystery authors play with time. Typically the murder occurs well before the midpoint of the book, but there is an information blackout at that point and the reader learns what happened then only on the last page.

If the last page were ripped out of the book, physicist Kater Murch, PhD, said, would the reader be better off guessing what happened by reading only up to the fatal incident or by reading the entire book?

The answer, so obvious in the case of the murder mystery, is less so in world of quantum mechanics, where indeterminacy is fundamental rather than contrived for our reading pleasure.

A Feb. 13, 2015 Washington University at St. Louis (WUSTL) news release by Diana Lutz, which originated the news item, describes the research,

Even if you know everything quantum mechanics can tell you about a quantum particle, said Murch, an assistant professor of physics in Arts & Sciences at Washington University in St. Louis, you cannot predict with certainty the outcome of a simple experiment to measure its state. All quantum mechanics can offer are statistical probabilities for the possible results.

The orthodox view is that this indeterminacy is not a defect of the theory, but rather a fact of nature. The particle’s state is not merely unknown, but truly undefined before it is measured. The act of measurement itself that forces the particle to collapse to a definite state.

It’s as if what we did today, changed what we did yesterday. And as this analogy suggests, the experimental results have spooky implications for  time and causality—at least in microscopic world to which quantum mechanics applies.

Until recently physicists could explore the quantum mechanical properties of single particles only through thought experiments, because any attempt to observe them directly caused them to shed their mysterious quantum properties.

But in the 1980s and 1990s physicists invented devices that allowed them to measure these fragile quantum systems so gently that they don’t immediately collapse to a definite state.

The device Murch uses to explore quantum space is a simple superconducting circuit that enters quantum space when it is cooled to near absolute zero. Murch’s team uses the bottom two energy levels of this qubit, the ground state and an excited state, as their model quantum system. Between these two states, there are an infinite number of quantum states that are superpositions, or combinations, of the ground and excited states.

The quantum state of the circuit is detected by putting it inside a microwave box. A few microwave photons are sent into the box, where their quantum fields interact with the superconducting circuit. So when the photons exit the box they bear information about the quantum system.

Crucially, these “weak,” off-resonance measurements do not disturb the qubit, unlike “strong” measurements with photons that are resonant with the energy difference between the two states, which knock the circuit into one or the other state.

In Physical Review Letters, Murch describes a quantum guessing game played with the qubit.

“We start each run by putting the qubit in a superposition of the two states,” he said. “Then we do a strong measurement but hide the result, continuing to follow the system with weak measurements.”

They then try to guess the hidden result, which is their version of the missing page of the murder mystery.

“Calculating forward, using the Born equation that expresses the probability of finding the system in a particular state, your odds of guessing right are only 50-50,” Murch said. “But you can also calculate backward using something called an effect matrix. Just take all the equations and flip them around. They still work and you can just run the trajectory backward.

“So there’s a backward-going trajectory and a forward-going trajectory and if we look at them both together and weight the information in both equally, we get something we call a hindsight prediction, or “retrodiction.”

The shattering thing about the retrodiction is that it is 90 percent accurate. When the physicists check it against the stored measurement of the system’s earlier state it is right nine times out of 10.

Going from a 50% accuracy rate to 90% is quite amazing and according to the news release, this has many implications,

The quantum guessing game suggests ways to make both quantum computing and the quantum control of open systems, such as chemical reactions, more robust. But it also has implications for much deeper problems in physics.

For one thing, it suggests that in the quantum world time runs both backward and forward whereas in the classical world it only runs forward.

“I always thought the measurement would resolve the time symmetry in quantum mechanics,” Murch said. “If we measure a particle in a superposition of states and it collapses into one of two states, well, that sounds like a process that goes forward in time.”

But in the quantum guessing experiment, time symmetry has returned. The improved odds imply the measured quantum state somehow incorporates information from the future as well as the past. And that implies that time, notoriously an arrow in the classical world, is a double-headed arrow in the quantum world.

“It’s not clear why in the real world, the world made up of many particles, time only goes forward and entropy always increases,” Murch said. “But many people are working on that problem and I expect it will be solved in a few years,” he said.

In a world where time is symmetric, however, is there such a thing as cause and effect? To find out, Murch proposes to run a qubit experiment that would set up feedback loops (which are chains of cause and effect) and try to run them both forward and backward.

“It takes 20 or 30 minutes to run one of these experiments,” Murch said, “several weeks to process it, and a year to scratch our heads to see if we’re crazy or not.”

“At the end of the day,” he said, “I take solace in the fact that we have a real experiment and real data that we plot on real curves.”

Here are links to and citations for the Physical Review paper and an earlier version of the paper,

 Prediction and retrodiction for a continuously monitored superconducting qubit by D. Tan, S. Weber, I. Siddiqi, K. Mølmer, K. W. Murch. arXiv.org > quant-ph > arXiv:1409.0510 (Submitted on 1 Sep 2014 (v1), last revised 10 Nov 2014 (this version, v2))

I last mentioned Kater Murch and his work in a July 31, 2014 post titled: Paths of desire: quantum style.

The quantum chemistry of nanomedicines

A Jan. 29, 2015 news item on Nanowerk provides an overview of the impact quantum chemical reactions may have on nanomedicines. Intriguingly, this line of query started with computations of white dwarf stars,

Quantum chemical calculations have been used to solve big mysteries in space. Soon the same calculations may be used to produce tomorrow’s cancer drugs.

Some years ago research scientists at the University of Oslo in Norway were able to show that the chemical bonding in the magnetic fields of small, compact stars, so-called white dwarf stars, is different from that on Earth. Their calculations pointed to a completely new bonding mechanism between two hydrogen atoms. The news attracted great attention in the media. The discovery, which in fact was made before astrophysicists themselves observed the first hydrogen molecules in white dwarf stars, was made by UiO’s Centre for Theoretical and Computational Chemistry. They based their work on accurate quantum chemical calculations of what happens when atoms and molecules are exposed to extreme conditions.

A Jan. 29, 2015 University of Oslo press release by Yngve Vogt, which originated the news item, offers a substantive description of molecules, electrons, and more for those of us whose last chemistry class is lost in the mists of time,

The research team is headed by Professor Trygve Helgaker, who for the last thirty years has taken the international lead on the design of a computer system for calculating quantum chemical reactions in molecules.

Quantum chemical calculations are needed to explain what happens to the electrons’ trajectories within a molecule.

Consider what happens when UV radiation sends energy-rich photons into your cells. This increases the energy level of the molecules. The outcome may well be that some of the molecules break up. This is exactly what happens when you sun-bathe.

“The extra energy will affect the behaviour of electrons and can destroy the chemical bonding within the molecule. This can only be explained by quantum chemistry. The quantum chemical models are used to produce a picture of the forces and tensions at play between the atoms and the electrons of a molecule, and of what is required for a molecule to dissociate,” says Trygve Helgaker.

The absurd world of the electrons

The quantum chemical calculations solve the Schrödinger equation for molecules. This equation is fundamental to all chemistry and describes the whereabouts of all electrons within a molecule. But here we need to pay attention, for things are really rather more complicated than that. Your high school physics teacher will have told you that electrons circle the atom. Things are not that simple, though, in the world of quantum physics. Electrons are not only particles, but waves as well. The electrons can be in many places at the same time. It’s impossible to keep track of their position. However, there is hope. Quantum chemical models describe the electrons’ statistical positions. In other words, they can establish the probable location of each electron.

The results of a quantum chemical calculation are often more accurate than what is achievable experimentally.

Among other things, the quantum chemical calculations can be used to predict chemical reactions. This means that the chemists will no longer have to rely on guesstimates in the lab. It is also possible to use quantum chemical calculations in order to understand what happens in experiments.

Enormous calculations

The calculations are very demanding.

“The Schrödinger equation is a highly complicated, partial differential equation, which cannot be accurately solved. Instead, we need to make do with heavy simulations”, says researcher Simen Kvaal.

The computations are so demanding that the scientists use one of the University’s fastest supercomputers.

“We are constantly stretching the boundaries of what is possible. We are restricted by the available machine capacity,” explains Helgaker.

Ten years ago it took two weeks to carry out the calculations for a molecule with 140 atoms. Now it can be done in two minutes.

“That’s 20,000 times faster than ten years ago. The computation process is now running 200 times faster because the computers have been doubling their speed every eighteen months. And the process is a further 100 times faster because the software has been undergoing constant improvement,” says senior engineer Simen Reine.

This year the research group has used 40 million CPU hours, of which twelve million were on the University’s supercomputer, which is fitted with ten thousand parallel processors. This allows ten thousand CPU hours to be over and done with in 60 minutes.

“We will always fill the computer’s free capacity. The higher the computational capacity, the bigger and more reliable the calculations.”

Thanks to ever faster computers, the quantum chemists are able to study ever larger molecules.

Today, it’s routine to carry out a quantum chemical calculation of what happens within a molecule of up to 400 atoms. By using simplified models it is possible to study molecules with several thousand atoms. This does, however, mean that some of the effects within the molecule are not being described in detail.

The researchers are now getting close to a level which enables them to study the quantum mechanics of living cells.

“This is exciting. The molecules of living cells may contain many hundred thousand atoms, but there is no need to describe the entire molecule using quantum mechanical principles. Consequently, we are already at a stage when we can help solve biological problems.”

There’s more from the press release which describes how this work could be applied in the future,

Hunting for the electrons of the insulin molecule

The chemists are thus able to combine sophisticated models with simpler ones. “This will always be a matter of what level of precision and detail you require. The optimal approach would have been to use the Schrödinger equation for everything.”

By way of compromise they can give a detailed description of every electron in some parts of the model, while in other parts they are only looking at average numbers.

Simen Reine has been using the team’s computer program, while working with Aarhus University [Finland], on a study of the insulin molecule. An insulin molecule consists of 782 atoms and 3,500 electrons.

“All electrons repel each other, while at the same time being pulled towards the atomic nuclei. The nuclei also repel each other. Nevertheless, the molecule remains stable. In order to study a molecule to a high level of precision, we therefore need to consider how all of the electrons move relative to one another. Such calculations are referred to as correlated and are very reliable.”

A complete correlated calculation of the insulin molecule takes nearly half a million CPU hours. If they were given the opportunity to run the program on the entire University’s supercomputer, the calculations would theoretically take two days.

“In ten years, we’ll be able to make these calculations in two minutes.”

Medically important

“Quantum chemical calculations can help describe phenomena at a level that may be difficult to access experimentally, but may also provide support for interpreting and planning experiments. Today, the calculations will be put to best use within the fields of molecular biology and biochemistry,” says Knut Fægri [vice-rector at the University of Oslo].

“Quantum chemistry is a fundamental theory which is important for explaining molecular events, which is why it is essential to our understanding of biological systems,” says [Associate Professor] Michele Cascella.

By way of an example, he refers to the analysis of enzymes. Enzymes are molecular catalysts that boost the chemical reactions within our cells.

Cascella also points to nanomedicines, which are drugs tasked with distributing medicine round our bodies in a much more accurate fashion.

“In nanomedicine we need to understand physical phenomena on a nano scale, forming as correct a picture as possible of molecular phenomena. In this context, quantum chemical calculations are important,” explains Michele Cascella.

Proteins and enzymes

Professor K. Kristoffer Andersson at the Department of Biosciences uses the simpler form of quantum chemical calculations to study the details of protein structures and the chemical atomic and electronic functions of enzymes.

“It is important to understand the chemical reaction mechanism, and how enzymes and proteins work. Quantum chemical calculations will teach us more about how proteins go about their tasks, step by step. We can also use the calculations to look at activation energy, i.e. how much energy is required to reach a certain state. It is therefore important to understand the chemical reaction patterns in biological molecules in order to develop new drugs,” says Andersson.

His research will also be useful in the search for cancer drugs. He studies radicals, which may be important to cancer. Among other things, he is looking at the metal ions function in proteins. These are ions with a large number of protons, neutrons and electrons.

Photosynthesis

Professor Einar Uggerud at the Department of Chemistry has uncovered an entirely new form of chemical bonding through sophisticated experiments and quantum chemical calculations.

Working with research fellow Glenn Miller, Professor Uggerud has found an unusually fragile key molecule, in a kite-shaped structure, consisting of magnesium, carbon and oxygen. The molecule may provide a new understanding of photosynthesis. Photosynthesis, which forms the basis for all life, converts CO2 into sugar molecules.

The molecule reacts so fast with water and other molecules that it has only been possible to study in isolation from other molecules, in a vacuum chamber.

“Time will tell whether the molecule really has an important connection with photosynthesis,” says Einar Uggerud.

I’m delighted with this explanation as it corrects my understanding of chemical bonds and helps me to better understand computational chemistry. Thank you University of Oslo and Yngve Vogt.

Finally, here’s a representation of an insulin molecule as understood by quantum computation,

QuantumInsulinMolecule

INSULIN: Working with Aarhus University, Simen Reine has calculated the tensions between the electrons and atoms of an insulin molecule. An insulin molecule consists of 782 atoms and 3,500 electrons. Illustration: Simen Reine-UiO

 

Atoms can be in two places at once

A Jan. 20, 2015 news item on Nanowerk offers a brief history of quantum mechanics,

Can a penalty kick simultaneously score a goal and miss? For very small objects, at least, this is possible: according to the predictions of quantum mechanics, microscopic objects can take different paths at the same time. The world of macroscopic objects follows other rules: the football always moves in a definite direction. But is this always correct? Physicists of the University of Bonn have constructed an experiment designed to possibly falsify this thesis. Their first experiment shows that Caesium atoms can indeed take two paths at the same time.

Almost 100 years ago physicists Werner Heisenberg, Max Born und Erwin Schrödinger created a new field of physics: quantum mechanics. Objects of the quantum world – according to quantum theory – no longer move along a single well-defined path. Rather, they can simultaneously take different paths and end up at different places at once.

A Jan. 20, 2015 Universität Bonn (University of Bonn) press release, which originated the news item, describes both the experiment and the thought process which led to the experiment,

At the level of atoms, it looks as if objects indeed obey quantum mechanical laws. Over the years, many experiments have confirmed quantum mechanical predictions. In our macroscopic daily experience, however, we witness a football flying along exactly one path; it never strikes the goal and misses at the same time.

“There are two different interpretations,” says Dr. Andrea Alberti of the Institute of Applied Physics of the University of Bonn. “Quantum mechanics allows superposition states of large, macroscopic objects. But these states are very fragile, even following the football with our eyes is enough to destroy the superposition and makes it follow a definite trajectory.”

But it could also be that footballs obey completely different rules than those applying for single atoms. “Let us talk about the macro-realistic view of the world,” Alberti explains. “According to this interpretation, the ball always moves on a specific trajectory, independent of our observation, and in contrast to the atom.”

In collaboration with Dr. Clive Emary of the University of Hull in the U.K., the Bonn team has come up with an experimental scheme that may help to answer this question. “The challenge was to develop a measurement scheme of the atoms’ positions which allows one to falsify macro-realistic theories,” adds Alberti.

The physicists describe their research in the journal “Physical Review X:” With two optical tweezers they grabbed a single Caesium atom and pulled it in two opposing directions. In the macro-realist’s world the atom would then be at only one of the two final locations. Quantum-mechanically, the atom would instead occupy a superposition of the two positions.

“We have now used indirect measurements to determine the final position of the atom in the most gentle way possible,” says the PhD student Carsten Robens. Even such an indirect measurement (see figure) significantly modified the result of the experiments. This observation excludes – falsifies, as Karl Popper would say more precisely – the possibility that Caesium atoms follow a macro-realistic theory. Instead, the experimental findings of the Bonn team fit well with an interpretation based on superposition states that get destroyed when the indirect measurement occurs. All that we can do is to accept that the atom has indeed taken different paths at the same time.

“This is not yet a proof that quantum mechanics hold for large objects,” cautions Alberti. “The next step is to separate the Caesium atom’s two positions by several millimetres. Should we still find the superposition in our experiment, the macro-realistic theory would suffer another setback.”

Here’s a link to and a citation for the paper,

Ideal negative measurements in quantum walks disprove theories based on classical trajectories by Carsten Robens, Wolfgang Alt, Dieter Meschede, Clive Emary, und Andrea Alberti. Physical Review X, 20.1.2015 (DOI: 10.1103/PhysRevX.5.011003)

This is an open access paper,

Paths of desire: quantum style

Shortcuts are also called paths of desire (and other terms too) by those who loathe them. It turns that humans and other animals are not the only ones who use shortcuts. From a July 30, 2014 news item on ScienceDaily,

Groundskeepers and landscapers hate them, but there is no fighting them. Called desire paths, social trails or goat tracks, they are the unofficial shortcuts people create between two locations when the purpose-built path doesn’t take them where they want to go.

There’s a similar concept in classical physics called the “path of least action.” If you throw a softball to a friend, the ball traces a parabola through space. It doesn’t follow a serpentine path or loop the loop because those paths have higher “actions” than the true path.

A July 30, 2014 Washington University in St. Louis (Missouri, US) news release (also on EurekAlert) by Diana Lutz, which originated the news item, describes the issues associated with undertaking this research,

Quantum particles can exist in a superposition of states, yet as soon as quantum particles are “touched” by the outside world, they lose this quantum strangeness and collapse to a classically permitted state. Because of this evasiveness, it wasn’t possible until recently to observe them in their quantum state.

But in the past 20 years, physicists have devised devices that isolate quantum systems from the environment and allow them to be probed so gently that they don’t immediately collapse. With these devices, scientists can at long last follow quantum systems into quantum territory, or state space.

Kater Murch, PhD, an assistant professor of physics at Washington University in St. Louis, and collaborators Steven Weber and Irfan Siddiqui of the Quantum Nanoelectronics Laboratory at the University of California, Berkeley, have used a superconducting quantum device to continuously record the tremulous paths a quantum system took between a superposition of states to one of two classically permitted states.

Because even gentle probing makes each quantum trajectory noisy, Murch’s team repeated the experiment a million times and examined which paths were most common. The quantum equivalent of the classical “least action” path — or the quantum device’s path of desire — emerged from the resulting cobweb of many paths, just as pedestrian desire paths gradually emerge after new sod is laid.

The experiments, the first continuous measurements of the trajectories of a quantum system between two points, are described in the cover article of the July 31 [2014] issue of Nature.

“We are working with the simplest possible quantum system,” Murch said. “But the understanding of quantum interactions we are gaining might eventually be useful for the quantum control of biological and chemical systems.

“Chemistry at its most basic level is described by quantum mechanics,” he said. “In the past 20 years, chemists have developed a technique called quantum control, where shaped laser pulses are used to drive chemical reactions — that is, to drive them between two quantum states. The chemists control the quantum field from the laser, and that field controls the dynamics of a reaction,” he said.

“Eventually, we’ll be able to control the dynamics of chemical reactions with lasers instead of just mixing reactant 1 with reactant 2 and letting the reaction evolve on its own,” he said.

An artificial atom The device Murch uses to explore quantum space is a simple superconducting circuit. Because it has quantized energy levels, or states, like an atom, it is sometimes called an artificial atom. Murch’s team uses the bottom two energy levels, the ground state and an excited state, as their model quantum system.

Between these two states, there are an infinite number of quantum states that are superpositions, or combinations, of the ground and excited states. In the past, these states would have been invisible to physicists because attempts to measure them would have caused the system to immediately collapse.

But Murch’s device allows the system’s state to be probed many times before it becomes an effectively classical system. The quantum state of the circuit is detected by putting it inside a microwave box. A very small number of microwave photons are sent into the box where their quantum fields interact with the superconducting circuit.

The microwaves are so far off resonance with the circuit that they cannot drive it between its ground and its excited state. So instead of being absorbed, they leave the box bearing information about the quantum system in the form of a phase shift (the position of the troughs and peaks of the photons’ wavefunctions).

Although there is information about the quantum system in the exiting microwaves, it is only a small amount of information.

“Every time we nudge the system, something different happens,” Murch said. “That’s because the photons we use to measure the quantum system are quantum mechanical as well and exhibit quantum fluctuations. So it takes many of these measurements to distinguish the system’s signal from the quantum fluctuations of the photons probing it.” Or, as physicists put it, these are weak measurements.

Murch compares these experiments to soccer matches, which are ultimately experiments to determine which team is better. But because so few goals are scored in soccer, and these are often lucky shots, the less skilled team has a good chance of winning. Or as Murch might put it, one soccer match is such a weak measurement of a team’s skill that it can’t be used to draw a statistically reliable conclusion about which team is more skilled.

Each time a team scores a goal, it becomes somewhat more likely that that team is the better team, but the teams would have to play many games or play for a very long time to know for sure. These fluctuations are what make soccer matches so exciting.

Murch is in essence able to observe millions of these matches, and from all the matches where team B wins, he can determine the most likely way a game that ends with a victory for team B will develop.

Despite the difficulties, the team did establish a path of desire,

“Before we started this experiment,” Murch said, ” I asked everybody in the lab what they thought the most likely path between quantum states would be. I drew a couple of options on the board: a straight line, a convex curve, a concave curve, a squiggly line . . . I took a poll, and we all guessed different options. Here we were, a bunch of quantum experts, and we had absolutely no intuition about the most likely path.”

Andrew N. Jordan of the University of Rochester and his students Areeya Chantasri and Justin Dressel inspired the study by devising a theory to predict the likely path. Their theory predicted that a convex curve Murch had drawn on the white board would be the correct path.

“When we looked at the data, we saw that the theorists were right. Our very clever collaborators had devised a ‘principle of least action’ that works in the quantum case,” Murch said.

They had found the quantum system’s line of desire mathematically and by calculation before many microwave photons trampled out the path in Murch’s lab.

Here’s an illustrated quantum path of desire’s experimental data,

Caption: A path of desire emerging from many trajectories between two points in quantum state space. Credit: Murch Lab/WUSTL

Caption: A path of desire emerging from many trajectories between two points in quantum state space.
Credit: Murch Lab/WUSTL

The University of Rochester, a collaborating institution on this research, issued a July 30, 2014 news release (also on EurekAlert) featuring this poetic allusion from one of the theorists,

Jordan [Andrew N. Jordan, professor of physics at the University of Rochester] compares the experiment to watching butterflies make their way one by one from a cage to nearby trees. “Each butterfly’s path is like a single run of the experiment,” said Jordan. “They are all starting from the same cage, the initial state, and ending in one of the trees, each being a different end state.” By watching the quantum equivalent of a million butterflies make the journey from cage to tree, the researchers were in effect able to predict the most likely path a butterfly took by observing which tree it landed on (known as post-selection in quantum physics measurements), despite the presence of a wind, or any disturbance that affects how it flies (which is similar to the effect measuring has on the system).

The theorists provided this illustration of the theory,

Caption: Measurement data showing the comparison with the 'most likely' path (in red) between initial and final quantum states (black dots). The measurements are shown on a representation referred to as a Bloch sphere. Credit: Areeya Chantasri Courtesy: University of Rochester

Caption: Measurement data showing the comparison with the ‘most likely’ path (in red) between initial and final quantum states (black dots). The measurements are shown on a representation referred to as a Bloch sphere.
Credit: Areeya Chantasri Courtesy: University of Rochester

The research study can be found here,

Mapping the optimal route between two quantum states by S. J. Weber, A. Chantasri, J. Dressel, A. N. Jordan, K. W. Murch & I. Siddiqi. Nature 511, 570–573 (31 July 2014) doi:10.1038/nature13559 Published online 30 July 2014

This paper is behind a paywall but there is a free preview via ReadCube Access.

Violating the 2nd law of thermodynamics—temporarily—at the nanoscale

For anyone unfamiliar with the laws of thermodynamics or anyone who enjoys some satire with their music, here’s the duo of Flanders & Swann with the ‘First and Second Law’ in a 1964 performance,

According to a March 31, 2014 news item on Nanowerk, it seems, contrary to scientific thought and Flanders & Swann, the 2nd law can be violated, for a time, albeit at the nanoscale,

Objects with sizes in the nanometer range, such as the molecular building blocks of living cells or nanotechnological devices, are continuously exposed to random collisions with surrounding molecules. In such fluctuating environments the fundamental laws of thermodynamics that govern our macroscopic world need to be rewritten. An international team of researchers from Barcelona, Zurich and Vienna found that a nanoparticle trapped with laser light temporarily violates the famous second law of thermodynamics, something that is impossible on human time and length scale.

A March 31, 2014 University of Vienna news release on EurekAlert, which originated the news item, describes the 2nd law and gives details about the research,

Watching a movie played in reverse often makes us laugh because unexpected and mysterious things seem to happen: glass shards lying on the floor slowly start to move towards each other, magically assemble and suddenly an intact glass jumps on the table where it gently gets to a halt. Or snow starts to from a water puddle in the sun, steadily growing until an entire snowman appears as if molded by an invisible hand. When we see such scenes, we immediately realize that according to our everyday experience something is out of the ordinary. Indeed, there are many processes in nature that can never be reversed. The physical law that captures this behavior is the celebrated second law of thermodynamics, which posits that the entropy of a system – a measure for the disorder of a system – never decreases spontaneously, thus favoring disorder (high entropy) over order (low entropy).

However, when we zoom into the microscopic world of atoms and molecules, this law softens up and looses its absolute strictness. Indeed, at the nanoscale the second law can be fleetingly violated. On rare occasions, one may observe events that never happen on the macroscopic scale such as, for example heat transfer from cold to hot which is unheard of in our daily lives. Although on average the second law of thermodynamics remains valid even in nanoscale systems, scientists are intrigued by these rare events and are investigating the meaning of irreversibility at the nanoscale.

Recently, a team of physicists of the University of Vienna, the Institute of Photonic Sciences in Barcelona and the Swiss Federal Institute of Technology in Zürich succeeded in accurately predicting the likelihood of events transiently violating the second law of thermodynamics. They immediately put the mathematical fluctuation theorem they derived to the test using a tiny glass sphere with a diameter of less than 100 nm levitated in a trap of laser light. Their experimental set-up allowed the research team to capture the nano-sphere and hold it in place, and, furthermore, to measure its position in all three spatial directions with exquisite precision. In the trap, the nano-sphere rattles around due to collisions with surrounding gas molecules. By a clever manipulation of the laser trap the scientists cooled the nano-sphere below the temperature of the surrounding gas and, thereby, put it into a non-equilibrium state. They then turned off the cooling and watched the particle relaxing to the higher temperature through energy transfer from the gas molecules. The researchers observed that the tiny glass sphere sometimes, although rarely, does not behave as one would expect according to the second law: the nano-sphere effectively releases heat to the hotter surroundings rather than absorbing the heat. The theory derived by the researchers to analyze the experiment confirms the emerging picture on the limitations of the second law on the nanoscale.

Given the theoretical descriptions of the applications mentioned in the news release, it sounds like at least one of them might be a ‘quantum computing project’,

The experimental and theoretical framework presented by the international research team in the renowned scientific journal Nature Nanotechnology has a wide range of applications. Objects with sizes in the nanometer range, such as the molecular building blocks of living cells or nanotechnological devices, are continuously exposed to a random buffeting due to the thermal motion of the molecules around them. As miniaturization proceeds to smaller and smaller scales nanomachines will experience increasingly random conditions. Further studies will be carried out to illuminate the fundamental physics of nanoscale systems out of equilibrium. The planned research will be fundamental to help us understand how nanomachines perform under these fluctuating conditions.

Here’s a link to and a citation for the paper,

Dynamic Relaxation of a Levitated Nanoparticle from a Non-Equilibrium Steady State by Jan Gieseler, Romain Quidant, Christoph Dellago, and Lukas Novotny. Nature Nanotechnology AOP, February 28, 2014. DOI: 10.1038/NNANO.2014.40

The paper is behind a paywall but a free preview is available via ReadCube access.

Fundamental mechanical behaviour of cellulose nanocrystals (aka nanocrystalline cellulose)

Emil Venere at Purdue University offers an excellent explanation of why there’s so much international interest in cellulose nanocrystals (CNC aka, nanocrystalline cellulose [NCC]) in his Dec. 16, 2013 Purdue University (Indiana, US) news release (also on EurekAlert), Note: A link has been removed,

The same tiny cellulose crystals that give trees and plants their high strength, light weight and resilience, have now been shown to have the stiffness of steel.

The nanocrystals might be used to create a new class of biomaterials with wide-ranging applications, such as strengthening construction materials and automotive components.

Calculations using precise models based on the atomic structure of cellulose show the crystals have a stiffness of 206 gigapascals, which is comparable to steel, said Pablo D. Zavattieri, a Purdue University assistant professor of civil engineering.

Here’s an image of the cellulose crystals being examined,

This transmission electron microscope image shows cellulose nanocrystals, tiny structures that give trees and plants their high strength, light weight and resilience. The nanocrystals might be used to create a new class of biomaterials that would have a wide range of applications. (Purdue Life Sciences Microscopy Center)

This transmission electron microscope image shows cellulose nanocrystals, tiny structures that give trees and plants their high strength, light weight and resilience. The nanocrystals might be used to create a new class of biomaterials that would have a wide range of applications. (Purdue Life Sciences Microscopy Center)

You’ll notice this image is not enhanced and made pretty as compared to the images in my Dec. 16, 2013 posting about Bristol University’s Art of Science competition. It takes a lot of work to turn the types of images scientists use into ‘art’.

Getting back to the CNC, this news release was probably written by someone who’s not familiar with the other work being done in the field (university press officers typically write about a wide range of topics and cannot hope to have in depth knowledge on each topic) and so it’s being presented as if it is brand new information. In fact, there has been several years work done in five other national jurisdictions that I know of (Sweden, Finland, Canada, Brazil, and Israel) and there are likely more. That’s not including other US states pursuing research in this area, notably Wisconsin.

What I (taking into account  my limitations) find particularly exciting in this work is the detail they’ve been able to determine and the reference to quantum mechanics. Here’s more from the news release (Note: Links have been removed),

“It is very difficult to measure the properties of these crystals experimentally because they are really tiny,” Zavattieri said. “For the first time, we predicted their properties using quantum mechanics.”

The nanocrystals are about 3 nanometers wide by 500 nanometers long – or about 1/1,000th the width of a grain of sand – making them too small to study with light microscopes and difficult to measure with laboratory instruments.

The findings represent a milestone in understanding the fundamental mechanical behavior of the cellulose nanocrystals.

“It is also the first step towards a multiscale modeling approach to understand and predict the behavior of individual crystals, the interaction between them, and their interaction with other materials,” Zavattieri said. “This is important for the design of novel cellulose-based materials as other research groups are considering them for a huge variety of applications, ranging from electronics and medical devices to structural components for the automotive, civil and aerospace industries.”

From an applications perspective (which is what excites so much international interest),

The cellulose nanocrystals represent a potential green alternative to carbon nanotubes for reinforcing materials such as polymers and concrete. Applications for biomaterials made from the cellulose nanocrystals might include biodegradable plastic bags, textiles and wound dressings; flexible batteries made from electrically conductive paper; new drug-delivery technologies; transparent flexible displays for electronic devices; special filters for water purification; new types of sensors; and computer memory.

Cellulose could come from a variety of biological sources including trees, plants, algae, ocean-dwelling organisms called tunicates, and bacteria that create a protective web of cellulose.

“With this in mind, cellulose nanomaterials are inherently renewable, sustainable, biodegradable and carbon-neutral like the sources from which they were extracted,” Moon said. “They have the potential to be processed at industrial-scale quantities and at low cost compared to other materials.”

Biomaterials manufacturing could be a natural extension of the paper and biofuels industries, using technology that is already well-established for cellulose-based materials.

“Some of the byproducts of the paper industry now go to making biofuels, so we could just add another process to use the leftover cellulose to make a composite material,” Moon said. “The cellulose crystals are more difficult to break down into sugars to make liquid fuel. So let’s make a product out of it, building on the existing infrastructure of the pulp and paper industry.”

Their surface can be chemically modified to achieve different surface properties.

“For example, you might want to modify the surface so that it binds strongly with a reinforcing polymer to make a new type of tough composite material, or you might want to change the chemical characteristics so that it behaves differently with its environment,” Moon said.

Zavattieri plans to extend his research to study the properties of alpha-chitin, a material from the shells of organisms including lobsters, crabs, mollusks and insects. Alpha-chitin appears to have similar mechanical properties as cellulose.

“This material is also abundant, renewable and waste of the food industry,” he said.

Here’s a link to and a citation for the paper,

Anisotropy of the Elastic Properties of Crystalline Cellulose Iβ from First Principles Density Functional Theory with Van der Waals Interactions by Fernando L. Dri, Louis G. Hector Jr., Robert J. Moon, Pablo D. Zavattieri.  Cellulose December 2013, Volume 20, Issue 6, pp 2703-2718. 10.1007/s10570-013-0071-8

This paper is behind a paywall although you can preview the first few pages.

Casimir and its reins: engineering nanostructures to control quantum effects

Thank you to whomever wrote this headline for the Oct. 22, 2013 US National Institute of Standards and Technology (NIST) news release, also on EurekAlert, titled: The Reins of Casimir: Engineered Nanostructures Could Offer Way to Control Quantum Effect … Once a Mystery Is Solved, for getting the word ‘reins’ correct.

I can no longer hold back my concern over the fact that there are three words that sound the same but have different meanings and one of those words is often mistakenly used in place of the other.

reins

reigns

rains

The first one, reins, refers to narrow leather straps used to control animals (usually horses), as per this picture, It’s also used as a verb to indicate situation where control must be exerted, e.g., the spending must be reined in.

Reining Sliding Stop Mannheim Maimarkt 2007 Date 01.05.2007 Source  Own work Author AllX [downloaded from http://en.wikipedia.org/wiki/File:Reining_slidingstop.jpg]

Reining Sliding Stop Mannheim Maimarkt 2007 Date 01.05.2007 Credit: AllX [downloaded from http://en.wikipedia.org/wiki/File:Reining_slidingstop.jpg]

 This ‘reign’ usually references people like these,

“Queen Elizabeth II greets employees on her walk from NASA’s Goddard Space Flight Center mission control to a reception in the center’s main auditorium in Greenbelt, Maryland where she was presented with a framed Hubble image by Congressman Steny Hoyer and Senator Barbara Mikulski. Queen Elizabeth II and her husband, Prince Philip, Duke of Edinburgh, visited the NASA Goddard Space Flight Center as one of the last stops on their six-day United States visit.” Credit: NASA/Bill Ingalls [downloaded from http://en.wikipedia.org/wiki/File:Elizabeth_II_greets_NASA_GSFC_employees,_May_8,_2007_edit.jpg]

“Queen Elizabeth II greets employees on her walk from NASA’s Goddard Space Flight Center mission control to a reception in the center’s main auditorium in Greenbelt, Maryland where she was presented with a framed Hubble image by Congressman Steny Hoyer and Senator Barbara Mikulski. Queen Elizabeth II and her husband, Prince Philip, Duke of Edinburgh, visited the NASA Goddard Space Flight Center as one of the last stops on their six-day United States visit.” Credit: NASA/Bill Ingalls [downloaded from http://en.wikipedia.org/wiki/File:Elizabeth_II_greets_NASA_GSFC_employees,_May_8,_2007_edit.jpg]

 And,

Thailand's King Bhumibol Adulyadej waves to well-wishers during a concert at Siriraj hospital in Bangkok on September 29, 2010. Credit: Government of Thailand [downloaded from http://en.wikipedia.org/wiki/File:King_Bhumibol_Adulyadej_2010-9-29.jpg]

Thailand’s King Bhumibol Adulyadej waves to well-wishers during a concert at Siriraj hospital in Bangkok on September 29, 2010. Credit: Government of Thailand [downloaded from http://en.wikipedia.org/wiki/File:King_Bhumibol_Adulyadej_2010-9-29.jpg]

Kings, Queens, etc. reign over or rule their subjects or they have reigns, i.e., the period during which they hold the position of queen/king, etc. There are also uses such as this one found in the song title ‘Love Reign O’er Me’ (Pete Townshend)

I’ve lost count of the times I’ve seen ‘reigns’ used in place of ‘reins’, the worst part being? I’ve caught myself making the mistake. So, a heartfelt thank you to the NIST news release writer for getting it right. As for the other ‘rains’, neither I not anyone else seems to make that mistake (so far as I’ve seen).

Now on to the news,

You might think that a pair of parallel plates hanging motionless in a vacuum just a fraction of a micrometer away from each other would be like strangers passing in the night—so close but destined never to meet. Thanks to quantum mechanics, you would be wrong.

Scientists working to engineer nanoscale machines know this only too well as they have to grapple with quantum forces and all the weirdness that comes with them. These quantum forces, most notably the Casimir effect, can play havoc if you need to keep closely spaced surfaces from coming together.

Controlling these effects may also be necessary for making small mechanical parts that never stick to each other, for building certain types of quantum computers, and for studying gravity at the microscale.

In trying to solve the problem of keeping closely spaced surfaces from coming together, the scientists uncovered another problem,

One of the insights of quantum mechanics is that no space, not even outer space, is ever truly empty. It’s full of energy in the form of quantum fluctuations, including fluctuating electromagnetic fields that seemingly come from nowhere and disappear just as fast.

Some of this energy, however, just isn’t able to “fit” in the submicrometer space between a pair of electromechanical contacts. More energy on the outside than on the inside results in a kind of “pressure” called the Casimir force, which can be powerful enough to push the contacts together and stick.

Prevailing theory does a good job describing the Casimir force between featureless, flat surfaces and even between most smoothly curved surfaces. However, according to NIST researcher and co-author of the paper, Vladimir Aksyuk, existing theory fails to predict the interactions they observed in their experiment.

“In our experiment, we measured the Casimir attraction between a gold-coated sphere and flat gold surfaces patterned with rows of periodic, flat-topped ridges, each less than 100 nanometers across, separated by somewhat wider gaps with deep sheer-walled sides,” says Aksyuk. “We wanted to see how a nanostructured metallic surface would affect the Casimir interaction, which had never been attempted with a metal surface before. Naturally, we expected that there would be reduced attraction between our grooved surface and the sphere, regardless of the distance between them, because the top of the grooved surface presents less total surface area and less material. However, we knew the Casimir force’s dependence on the surface shape is not that simple.”

Indeed, what they found was more complicated.

According to Aksyuk, when they increased the separation between the surface of the sphere and the grooved surface, the researchers found that the Casimir attraction decreased much more quickly than expected. When they moved the sphere farther away, the force fell by a factor of two below the theoretically predicted value. When they moved the sphere surface close to the ridge tops, the attraction per unit of ridge top surface area increased.

“Theory can account for the stronger attraction, but not for the too-rapid weakening of the force with increased separation,” says Aksyuk. “So this is new territory, and the physics community is going to need to come up with a new model to describe it.”

For the curious, here’s a link to and a citation for the research paper,

Strong Casimir force reduction through metallic surface nanostructuring by Francesco Intravaia, Stephan Koev, Il Woong Jung, A. Alec Talin, Paul S. Davids, Ricardo S. Decca, Vladimir A. Aksyuk, Diego A. R. Dalvit, & Daniel López. Nature Communications 4, Article number: 2515 doi:10.1038/ncomms3515 Published 27 September 2013.

This article is open access.

Testing ‘Schroedinger’s cat’ on everyday objects at the University of Calgary (Canada)

For decades physicists have been grappling with the question of why the rules for quantum mechanics/physics are so different from classical physics while they try to unify the theories into one coherent explanation for why things are the way they are. At the same time, they’ve also been trying to test how the rules of quantum mechanics might apply to everyday objects and it seems a team from the University of Calgary (Alberta, Canada) have made a breakthrough.

The July 21, 2013 University of Calgary news release on EurekAlert provides an explanation of Schroedinger’s thought experiment (the dead/alive cat), quantum mechanics, and difficulties testing the theory on everyday objects thus helping those of us without that knowledge to better understand the breakthrough,

In contrast to our everyday experience, quantum physics allows for particles to be in two states at the same time — so-called quantum superpositions. A radioactive nucleus, for example, can simultaneously be in a decayed and non-decayed state.

Applying these quantum rules to large objects leads to paradoxical and even bizarre consequences. To emphasize this, Erwin Schroedinger, one of the founding fathers of quantum physics, proposed in 1935 a thought experiment involving a cat that could be killed by a mechanism triggered by the decay of a single atomic nucleus. If the nucleus is in a superposition of decayed and non-decayed states, and if quantum physics applies to large objects, the belief is that the cat will be simultaneously dead and alive.

While quantum systems with properties akin to ‘Schroedinger’s cat’ have been achieved at a micro level, the application of this principle to everyday macro objects has proved to be difficult to demonstrate.

“This is because large quantum objects are extremely fragile and tend to disintegrate when subjected to any interaction with the environment,” explains Lvovsky [professor Alex Lvovsky].

Now for the breakthrough (from the news release),

The breakthrough achieved by Calgary quantum physicists is that they were able to contrive a quantum state of light that consists of a hundred million light quanta (photons) and can even be seen by the naked eye. In their state, the “dead” and “alive” components of the “cat” correspond to quantum states that differ by tens of thousands of photons.

“The laws of quantum mechanics which govern the microscopic world are very different from classical physics that rules over large objects such as live beings,” explains lead author Lvovsky. “The challenge is to understand where to draw the line and explore whether such a line exists at all. Those are the questions our experiment sheds light on,” he states.

While the findings are promising, study co-author Simon [professor Christoph Simon] admits that many questions remain unanswered.

“We are still very far from being able to do this with a real cat,” he says. “But this result suggests there is ample opportunity for progress in that direction.”

They want to try this on a real live  cat? hmmm

For those who’d like to satisfy their curiosity further, here’s a link to and a citation for the published paper,

Observation of micro–macro entanglement of light by A. I. Lvovsky, R. Ghobadi, A. Chandra, A. S. Prasad & C. Simon. Nature Physics (2013) doi:10.1038/nphys2682 Published online 21 July 2013

This paper is behind a paywall.

The best atomic movie ever from the University of Toronto (Canada)

To date, the real-time video, recorded by scientists from the University of Toronto, of atoms undergoing a transformation to become a new structure offers the best resolution yet, according to an Apr. 18, 2013 news item on Azonano,

“It’s the first look at how chemistry and biology involve just a few key motions for even the most complex systems,” says U of T [University of Toronto] chemistry and physics professor R. J. Dwayne Miller, principal investigator of the study. “There is an enormous reduction in complexity at the defining point, the transition state region, which makes chemical processes transferrable from one type of molecule to another. This is how new drugs or materials are made.”

Miller, who holds a joint appointment as director of the Max Planck Research Group for Structural Dynamics at the Centre for Free Electron Laser Science, conducted the research with colleagues from institutions in Germany and Japan. He says nature uses this reduction principle at transition states to breathe life into otherwise inanimate matter.

“The first atomic movies were very grainy, much like the first motion pictures,” says Miller. “The new movies are so clear one could dare say they are becoming beautiful to behold, especially when you remember you are looking at atoms moving on the fly. We’ve captured them at an incredibly fast rate of less than 1 millionth of a millionth of a second per frame.”

In the Apr. 17, 2013 University of Toronto news release, which originated the news item, Miller provides a description of the complexity,

To help illuminate what’s going on here,  Miller explains that with two atoms there is only one possible coordinate or dimension for following the chemical pathway. With three atoms, two dimensions are now needed. However, with a complex molecule, it would be expected that hundreds or even thousands of dimensions would be required to map all possible trajectories of the atoms.

“In this case, chemistry would be a completely new problem for every molecule,” says Miller. “But somehow there is an enormous reduction in dimensions to just a few motions, and we are now able to see exactly how this works at the atomic level of detail.”

Mapping molecular motions -- the "magic" of Chemistry revealed. Despite the enormous number of possible arrangements of atoms during a structural transition, such as occurs with changes in charge distribution or chemical processes, the interconversion from one structure to another reduces to a few key types of motions.  This enormous reduction in dimensionality is what makes chemical concepts transferable from one molecule to another and has enabled chemists to synthesize nearly any molecule desired, for new drugs to infusing new material properties. This movie gives a direct atomic level view of this enormous reduction in complexity.  The specific trajectories along 3 different coordinates, as highlighted in the movie, are shown as projections (right view) on a cube.  The key atomic motions can be mapped on to 3 highly simplified coordinates -- the magic of chemistry in its full atomic splendour. Credit: Lai Chung Liu, University of Toronto

Mapping molecular motions — the “magic” of Chemistry revealed. Despite the enormous number of possible arrangements of atoms during a structural transition, such as occurs with changes in charge distribution or chemical processes, the interconversion from one structure to another reduces to a few key types of motions. This enormous reduction in dimensionality is what makes chemical concepts transferable from one molecule to another and has enabled chemists to synthesize nearly any molecule desired, for new drugs to infusing new material properties. This movie gives a direct atomic level view of this enormous reduction in complexity. The specific trajectories along 3 different coordinates, as highlighted in the movie, are shown as projections (right view) on a cube. The key atomic motions can be mapped on to 3 highly simplified coordinates — the magic of chemistry in its full atomic splendour.
Credit: Lai Chung Liu, University of Toronto

Unfortunately, I was not able to successfully bring over the movie but you can try accessing it from here.

Mechanics of quantum kissing

“It is as if you can kiss without quite touching lips,” says Professor Jeremy Baumberg from the University of Cambridge Cavendish Laboratory in the University of Cambridge’s Nov. 7, 2012 news release about quantum electron jumps,

Even empty gaps have a colour. Now scientists have shown that quantum jumps of electrons can change the colour of gaps between nano-sized balls of gold. The new results, published today in the journal Nature, set a fundamental quantum limit on how tightly light can be trapped.

The team from the Universities of Cambridge, the Basque Country and Paris have combined tour de force experiments with advanced theories to show how light interacts with matter at nanometre sizes. The work shows how they can literally see quantum mechanics in action in air at room temperature.

As for the kissing, it all starts with metal and jumping electrons,

Because electrons in a metal move easily, shining light onto a tiny crack pushes electric charges onto and off each crack face in turn, at optical frequencies. The oscillating charge across the gap produces a ‘plasmonic’ colour for the ghostly region in-between, but only when the gap is small enough.

Team leader Professor Jeremy Baumberg from the University of Cambridge Cavendish Laboratory suggests we think of this like the tension building between a flirtatious couple staring into each other’s eyes. As their faces get closer the tension mounts, and only a kiss discharges this energy.

H/T to the Nov. 7, 2012 news item on ScienceDaily where I first learned of quantum kissing,

In the new experiments, the gap is shrunk below 1nm (1 billionth of a metre) which strongly reddens the gap colour as the charge builds up. However because electrons can jump across the gap by quantum tunnelling, the charge can drain away when the gap is below 0.35nm, seen as a blue-shifting of the colour. …

Prof Javier Aizpurua, leader of the theoretical team from San Sebastian complains: “Trying to model so many electrons oscillating inside the gold just cannot be done with existing theories.” He has had to fuse classical and quantum views of the world to even predict the colour shifts seen in experiment.

The new insights from this work suggest ways to measure the world down to the scale of single atoms and molecules, and strategies to make useful tiny devices.

Something to think about the next time you kiss.