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Quantum supremacy

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This supremacy, refers to an engineering milestone and a October 23, 2019 news item on ScienceDaily announces the milestone has been reached,

Researchers in UC [University of California] Santa Barbara/Google scientist John Martinis’ group have made good on their claim to quantum supremacy. Using 53 entangled quantum bits (“qubits”), their Sycamore computer has taken on — and solved — a problem considered intractable for classical computers.

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An October 23, 2019 UC Santa Barbara news release (also on EurekAlert) by Sonia Fernandez, which originated the news item, delves further into the work,

“A computation that would take 10,000 years on a classical supercomputer took 200 seconds on our quantum computer,” said Brooks Foxen, a graduate student researcher in the Martinis Group. “It is likely that the classical simulation time, currently estimated at 10,000 years, will be reduced by improved classical hardware and algorithms, but, since we are currently 1.5 trillion times faster, we feel comfortable laying claim to this achievement.”

The feat is outlined in a paper in the journal Nature.

The milestone comes after roughly two decades of quantum computing research conducted by Martinis and his group, from the development of a single superconducting qubit to systems including architectures of 72 and, with Sycamore, 54 qubits (one didn’t perform) that take advantage of the both awe-inspiring and bizarre properties of quantum mechanics.

“The algorithm was chosen to emphasize the strengths of the quantum computer by leveraging the natural dynamics of the device,” said Ben Chiaro, another graduate student researcher in the Martinis Group. That is, the researchers wanted to test the computer’s ability to hold and rapidly manipulate a vast amount of complex, unstructured data.

“We basically wanted to produce an entangled state involving all of our qubits as quickly as we can,” Foxen said, “and so we settled on a sequence of operations that produced a complicated superposition state that, when measured, returns bitstring with a probability determined by the specific sequence of operations used to prepare that particular superposition. The exercise, which was to verify that the circuit’s output correspond to the equence used to prepare the state, sampled the quantum circuit a million times in just a few minutes, exploring all possibilities — before the system could lose its quantum coherence.

‘A complex superposition state’

“We performed a fixed set of operations that entangles 53 qubits into a complex superposition state,” Chiaro explained. “This superposition state encodes the probability distribution. For the quantum computer, preparing this superposition state is accomplished by applying a sequence of tens of control pulses to each qubit in a matter of microseconds. We can prepare and then sample from this distribution by measuring the qubits a million times in 200 seconds.”

“For classical computers, it is much more difficult to compute the outcome of these operations because it requires computing the probability of being in any one of the 2^53 possible states, where the 53 comes from the number of qubits — the exponential scaling is why people are interested in quantum computing to begin with,” Foxen said. “This is done by matrix multiplication, which is expensive for classical computers as the matrices become large.”

According to the new paper, the researchers used a method called cross-entropy benchmarking to compare the quantum circuit’s output (a “bitstring”) to its “corresponding ideal probability computed via simulation on a classical computer” to ascertain that the quantum computer was working correctly.

“We made a lot of design choices in the development of our processor that are really advantageous,” said Chiaro. Among these advantages, he said, are the ability to experimentally tune the parameters of the individual qubits as well as their interactions.

While the experiment was chosen as a proof-of-concept for the computer, the research has resulted in a very real and valuable tool: a certified random number generator. Useful in a variety of fields, random numbers can ensure that encrypted keys can’t be guessed, or that a sample from a larger population is truly representative, leading to optimal solutions for complex problems and more robust machine learning applications. The speed with which the quantum circuit can produce its randomized bit string is so great that there is no time to analyze and “cheat” the system.

“Quantum mechanical states do things that go beyond our day-to-day experience and so have the potential to provide capabilities and application that would otherwise be unattainable,” commented Joe Incandela, UC Santa Barbara’s vice chancellor for research. “The team has demonstrated the ability to reliably create and repeatedly sample complicated quantum states involving 53 entangled elements to carry out an exercise that would take millennia to do with a classical supercomputer. This is a major accomplishment. We are at the threshold of a new era of knowledge acquisition.”

Looking ahead

With an achievement like “quantum supremacy,” it’s tempting to think that the UC Santa Barbara/Google researchers will plant their flag and rest easy. But for Foxen, Chiaro, Martinis and the rest of the UCSB/Google AI Quantum group, this is just the beginning.

“It’s kind of a continuous improvement mindset,” Foxen said. “There are always projects in the works.” In the near term, further improvements to these “noisy” qubits may enable the simulation of interesting phenomena in quantum mechanics, such as thermalization, or the vast amount of possibility in the realms of materials and chemistry.

In the long term, however, the scientists are always looking to improve coherence times, or, at the other end, to detect and fix errors, which would take many additional qubits per qubit being checked. These efforts have been running parallel to the design and build of the quantum computer itself, and ensure the researchers have a lot of work before hitting their next milestone.

“It’s been an honor and a pleasure to be associated with this team,” Chiaro said. “It’s a great collection of strong technical contributors with great leadership and the whole team really synergizes well.”

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

Quantum supremacy using a programmable superconducting processor by Frank Arute, Kunal Arya, Ryan Babbush, Dave Bacon, Joseph C. Bardin, Rami Barends, Rupak Biswas, Sergio Boixo, Fernando G. S. L. Brandao, David A. Buell, Brian Burkett, Yu Chen, Zijun Chen, Ben Chiaro, Roberto Collins, William Courtney, Andrew Dunsworth, Edward Farhi, Brooks Foxen, Austin Fowler, Craig Gidney, Marissa Giustina, Rob Graff, Keith Guerin, Steve Habegger, Matthew P. Harrigan, Michael J. Hartmann, Alan Ho, Markus Hoffmann, Trent Huang, Travis S. Humble, Sergei V. Isakov, Evan Jeffrey, Zhang Jiang, Dvir Kafri, Kostyantyn Kechedzhi, Julian Kelly, Paul V. Klimov, Sergey Knysh, Alexander Korotkov, Fedor Kostritsa, David Landhuis, Mike Lindmark, Erik Lucero, Dmitry Lyakh, Salvatore Mandrà, Jarrod R. McClean, Matthew McEwen, Anthony Megrant, Xiao Mi, Kristel Michielsen, Masoud Mohseni, Josh Mutus, Ofer Naaman, Matthew Neeley, Charles Neill, Murphy Yuezhen Niu, Eric Ostby, Andre Petukhov, John C. Platt, Chris Quintana, Eleanor G. Rieffel, Pedram Roushan, Nicholas C. Rubin, Daniel Sank, Kevin J. Satzinger, Vadim Smelyanskiy, Kevin J. Sung, Matthew D. Trevithick, Amit Vainsencher, Benjamin Villalonga, Theodore White, Z. Jamie Yao, Ping Yeh, Adam Zalcman, Hartmut Neven & John M. Martinis. Nature volume 574, pages505–510 (2019) DOI: https://doi.org/10.1038/s41586-019-1666-5 Issue Date 24 October 2019

This paper appears to be open access.

Quantum back action and devil’s play

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I always appreciate a reference to James Clerk Maxwell’s demon thought experiment (you can find out about it in the Maxwell’s demon Wikipedia entry). This time it comes from physicist  Kater Murch in a July 23, 2018 Washington University in St. Louis (WUSTL) news release (published July 25, 2018 on EurekAlert) written by Brandie Jefferson (offering a good explanation of the thought experiment and more),

Thermodynamics is one of the most human of scientific enterprises, according to Kater Murch, associate professor of physics in Arts & Sciences at Washington University in St. Louis.

“It has to do with our fascination of fire and our laziness,” he said. “How can we get fire” — or heat — “to do work for us?”

Now, Murch and colleagues have taken that most human enterprise down to the intangible quantum scale — that of ultra low temperatures and microscopic systems — and discovered that, as in the macroscopic world, it is possible to use information to extract work.

There is a catch, though: Some information may be lost in the process.

“We’ve experimentally confirmed the connection between information in the classical case and the quantum case,” Murch said, “and we’re seeing this new effect of information loss.”

The results were published in the July 20 [2018] issue of Physical Review Letters.

The international team included Eric Lutz of the University of Stuttgart; J. J. Alonzo of the University of Erlangen-Nuremberg; Alessandro Romito of Lancaster University; and Mahdi Naghiloo, a Washington University graduate research assistant in physics.

That we can get energy from information on a macroscopic scale was most famously illustrated in a thought experiment known as Maxwell’s Demon. [emphasis mine] The “demon” presides over a box filled with molecules. The box is divided in half by a wall with a door. If the demon knows the speed and direction of all of the molecules, it can open the door when a fast-moving molecule is moving from the left half of the box to the right side, allowing it to pass. It can do the same for slow particles moving in the opposite direction, opening the door when a slow-moving molecule is approaching from the right, headed left. ­

After a while, all of the quickly-moving molecules are on the right side of the box. Faster motion corresponds to higher temperature. In this way, the demon has created a temperature imbalance, where one side of the box is hotter. That temperature imbalance can be turned into work — to push on a piston as in a steam engine, for instance. At first the thought experiment seemed to show that it was possible create a temperature difference without doing any work, and since temperature differences allow you to extract work, one could build a perpetual motion machine — a violation of the second law of thermodynamics.

“Eventually, scientists realized that there’s something about the information that the demon has about the molecules,” Murch said. “It has a physical quality like heat and work and energy.”

His team wanted to know if it would be possible to use information to extract work in this way on a quantum scale, too, but not by sorting fast and slow molecules. If a particle is in an excited state, they could extract work by moving it to a ground state. (If it was in a ground state, they wouldn’t do anything and wouldn’t expend any work).

But they wanted to know what would happen if the quantum particles were in an excited state and a ground state at the same time, analogous to being fast and slow at the same time. In quantum physics, this is known as a superposition.

“Can you get work from information about a superposition of energy states?” Murch asked. “That’s what we wanted to find out.”

There’s a problem, though. On a quantum scale, getting information about particles can be a bit … tricky.

“Every time you measure the system, it changes that system,” Murch said. And if they measured the particle to find out exactly what state it was in, it would revert to one of two states: excited, or ground.

This effect is called quantum backaction. To get around it, when looking at the system, researchers (who were the “demons”) didn’t take a long, hard look at their particle. Instead, they took what was called a “weak observation.” It still influenced the state of the superposition, but not enough to move it all the way to an excited state or a ground state; it was still in a superposition of energy states. This observation was enough, though, to allow the researchers track with fairly high accuracy, exactly what superposition the particle was in — and this is important, because the way the work is extracted from the particle depends on what superposition state it is in.

To get information, even using the weak observation method, the researchers still had to take a peek at the particle, which meant they needed light. So they sent some photons in, and observed the photons that came back.

“But the demon misses some photons,” Murch said. “It only gets about half. The other half are lost.” But — and this is the key — even though the researchers didn’t see the other half of the photons, those photons still interacted with the system, which means they still had an effect on it. The researchers had no way of knowing what that effect was.

They took a weak measurement and got some information, but because of quantum backaction, they might end up knowing less than they did before the measurement. On the balance, that’s negative information.

And that’s weird.

“Do the rules of thermodynamics for a macroscopic, classical world still apply when we talk about quantum superposition?” Murch asked. “We found that yes, they hold, except there’s this weird thing. The information can be negative.

“I think this research highlights how difficult it is to build a quantum computer,” Murch said.

“For a normal computer, it just gets hot and we need to cool it. In the quantum computer you are always at risk of losing information.”

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

Information Gain and Loss for a Quantum Maxwell’s Demon by M. Naghiloo, J. J. Alonso, A. Romito, E. Lutz, and K. W. Murch. Phys. Rev. Lett. 121, 030604 (Vol. 121, Iss. 3 — 20 July 2018) DOI:https://doi.org/10.1103/PhysRevLett.121.030604 Published 17 July 2018

© 2018 American Physical Society

This paper is behind a paywall.

An atom without properties?

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There’s rather intriguing Swiss research into atoms and so-called Bell Correlations according to an April 21, 2016 news item on ScienceDaily,

The microscopic world is governed by the rules of quantum mechanics, where the properties of a particle can be completely undetermined and yet strongly correlated with those of other particles. Physicists from the University of Basel have observed these so-called Bell correlations for the first time between hundreds of atoms. Their findings are published in the scientific journal Science.

Everyday objects possess properties independently of each other and regardless of whether we observe them or not. Einstein famously asked whether the moon still exists if no one is there to look at it; we answer with a resounding yes. This apparent certainty does not exist in the realm of small particles. The location, speed or magnetic moment of an atom can be entirely indeterminate and yet still depend greatly on the measurements of other distant atoms.

An April 21, 2016 University of Basel (Switzerland) press release (also on EurekAlert), which originated the news item, provides further explanation,

With the (false) assumption that atoms possess their properties independently of measurements and independently of each other, a so-called Bell inequality can be derived. If it is violated by the results of an experiment, it follows that the properties of the atoms must be interdependent. This is described as Bell correlations between atoms, which also imply that each atom takes on its properties only at the moment of the measurement. Before the measurement, these properties are not only unknown – they do not even exist.

A team of researchers led by professors Nicolas Sangouard and Philipp Treutlein from the University of Basel, along with colleagues from Singapore, have now observed these Bell correlations for the first time in a relatively large system, specifically among 480 atoms in a Bose-Einstein condensate. Earlier experiments showed Bell correlations with a maximum of four light particles or 14 atoms. The results mean that these peculiar quantum effects may also play a role in larger systems.

Large number of interacting particles

In order to observe Bell correlations in systems consisting of many particles, the researchers first had to develop a new method that does not require measuring each particle individually – which would require a level of control beyond what is currently possible. The team succeeded in this task with the help of a Bell inequality that was only recently discovered. The Basel researchers tested their method in the lab with small clouds of ultracold atoms cooled with laser light down to a few billionths of a degree above absolute zero. The atoms in the cloud constantly collide, causing their magnetic moments to become slowly entangled. When this entanglement reaches a certain magnitude, Bell correlations can be detected. Author Roman Schmied explains: “One would expect that random collisions simply cause disorder. Instead, the quantum-mechanical properties become entangled so strongly that they violate classical statistics.”

More specifically, each atom is first brought into a quantum superposition of two states. After the atoms have become entangled through collisions, researchers count how many of the atoms are actually in each of the two states. This division varies randomly between trials. If these variations fall below a certain threshold, it appears as if the atoms have ‘agreed’ on their measurement results; this agreement describes precisely the Bell correlations.

New scientific territory

The work presented, which was funded by the National Centre of Competence in Research Quantum Science and Technology (NCCR QSIT), may open up new possibilities in quantum technology; for example, for generating random numbers or for quantum-secure data transmission. New prospects in basic research open up as well: “Bell correlations in many-particle systems are a largely unexplored field with many open questions – we are entering uncharted territory with our experiments,” says Philipp Treutlein.

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

Bell correlations in a Bose-Einstein condensate by Roman Schmied, Jean-Daniel Bancal, Baptiste Allard, Matteo Fadel, Valerio Scarani, Philipp Treutlein, Nicolas Sangouard. Science  22 Apr 2016: Vol. 352, Issue 6284, pp. 441-444 DOI: 10.1126/science.aad8665

This paper is behind a paywall.

Star Trek, Schrödinger’s cat, quantum entanglement, and more in memory teleportation scheme

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A Jan. 13, 2016 news item on Nanowerk introduces Star Trek and Schrödinger’s cat as means to explain a quantum teleportation theory (Note: A link has been removed),

In “Star Trek”, a transporter can teleport a person from one location to a remote location without actually making the journey along the way. Such a transporter has fascinated many people. Quantum teleportation shares several features of the transporter and is one of the most important protocols in quantum information.

In a recent study (“Quantum superposition, entanglement, and state teleportation of a microorganism on an electromechanical oscillator”), Prof. Tongcang Li at Purdue University [US] and Dr. Zhang-qi Yin at Tsinghua University [China] proposed the first scheme to use electromechanical oscillators and superconducting circuits to teleport the internal quantum state (memory) and center-of-mass motion state of a microorganism.

They also proposed a scheme to create a Schrödinger’s cat state in which a microorganism can be in two places at the same time. This is an important step towards potentially teleporting an organism in future.

A Jan. 13, 2016 Science China Press news release on EurekAlert, which originated the news item, expands on the theme,

In 1935, Erwin Schrödinger proposed a famous thought experiment to prepare a cat in a superposition of both alive and dead states. The possibility of an organism to be in a superposition state dramatically reveals the profound consequences of quantum mechanics, and has attracted broad interests. Physicists have made great efforts in many decades to investigate macroscopic quantum phenomena. So far, matter-wave interference of electrons, atoms, and molecules (such as C60) have been observed. Recently, quantum ground state cooling and the creation of superposition states of mechanical oscillators have been realized. For example, a group in Colorado, US has cooled the vibration of a 15-micrometer-diameter aluminum membrane to quantum ground state, and entangled its motion with microwave photons. However, quantum superposition of an entire organism has not been realized. Meanwhile, there have been many breakthroughs in quantum teleportation since its first experimental realization in 1997 with a single photon. Besides photons, quantum teleportation with atoms, ions, and superconducting circuits have been demonstrated. In 2015, a group at University of Science and Technology of China demonstrated the quantum teleportation of multiple degrees of freedom of a single photon. However, existing experiments are still far away from teleporting an organism or the state of an organism.

In a recent study, Tongcang Li and Zhang-qi Yin propose to put a bacterium on top of an electromechanical membrane oscillator integrated with a superconducting circuit to prepare quantum superposition state of a microorganism and teleport its quantum state. A microorganism with a mass much smaller than the mass of the electromechanical membrane will not significantly affect the quality factor of the membrane and can be cooled to the quantum ground state together with the membrane. Quantum superposition and teleportation of its center-of-mass motion state can be realized with the help of superconducting microwave circuits. With a strong magnetic field gradient, the internal states of a microorganism, such as the electron spin of a glycine radical, can be entangled with its center-of-mass motion and be teleported to a remote microorganism. Since internal states of an organism contain information, this proposal provides a scheme for teleporting information or memories between two remote organisms.

The proposed setup is also a quantum-limited magnetic resonance force microscope. It not only can detect the existence of single electron spins (associated to protein defects or DNA defects) like conventional MRFM, but also can coherently manipulate and detect the quantum states of electron spins. It enables some isolated electron spins that could not be read out with optical or electrical methods to be used as quantum memory for quantum information.

Li says “We propose a straightforward method to put a microorganism in two places at the same time, and provide a scheme to teleport the quantum state of a microorganism. I hope our unconventional work will inspire more people to think seriously about quantum teleportation of a microorganism and its potential applications in future.” Yin says “Our work also provides insights for future studies about the effects of biochemical reactions in the wave function collapses of quantum superposition states of an organism.”

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

Quantum superposition, entanglement, and state teleportation of a microorganism on an electromechanical oscillator by Tongcang Li and Zhang-Qi Yin. Science Bulletin pp 1-9 DOI: 10.1007/s11434-015-0990-x First online: 11 January 2016

This paper is behind a paywall.

D-Wave upgrades Google’s quantum computing capabilities

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Vancouver-based (more accurately, Burnaby-based) D-Wave systems has scored a coup as key customers have upgraded from a 512-qubit system to a system with over 1,000 qubits. (The technical breakthrough and concomitant interest from the business community was mentioned here in a June 26, 2015 posting.) As for the latest business breakthrough, here’s more from a Sept. 28, 2015 D-Wave press release,

D-Wave Systems Inc., the world’s first quantum computing company, announced that it has entered into a new agreement covering the installation of a succession of D-Wave systems located at NASA’s Ames Research Center in Moffett Field, California. This agreement supports collaboration among Google, NASA and USRA (Universities Space Research Association) that is dedicated to studying how quantum computing can advance artificial intelligence and machine learning, and the solution of difficult optimization problems. The new agreement enables Google and its partners to keep their D-Wave system at the state-of-the-art for up to seven years, with new generations of D-Wave systems to be installed at NASA Ames as they become available.

“The new agreement is the largest order in D-Wave’s history, and indicative of the importance of quantum computing in its evolution toward solving problems that are difficult for even the largest supercomputers,” said D-Wave CEO Vern Brownell. “We highly value the commitment that our partners have made to D-Wave and our technology, and are excited about the potential use of our systems for machine learning and complex optimization problems.”

Cade Wetz’s Sept. 28, 2015 article for Wired magazine provides some interesting observations about D-Wave computers along with some explanations of quantum computing (Note: Links have been removed),

Though the D-Wave machine is less powerful than many scientists hope quantum computers will one day be, the leap to 1000 qubits represents an exponential improvement in what the machine is capable of. What is it capable of? Google and its partners are still trying to figure that out. But Google has said it’s confident there are situations where the D-Wave can outperform today’s non-quantum machines, and scientists at the University of Southern California [USC] have published research suggesting that the D-Wave exhibits behavior beyond classical physics.

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A quantum computer operates according to the principles of quantum mechanics, the physics of very small things, such as electrons and photons. In a classical computer, a transistor stores a single “bit” of information. If the transistor is “on,” it holds a 1, and if it’s “off,” it holds a 0. But in quantum computer, thanks to what’s called the superposition principle, information is held in a quantum system that can exist in two states at the same time. This “qubit” can store a 0 and 1 simultaneously.

Two qubits, then, can hold four values at any given time (00, 01, 10, and 11). And as you keep increasing the number of qubits, you exponentially increase the power of the system. The problem is that building a qubit is a extreme difficult thing. If you read information from a quantum system, it “decoheres.” Basically, it turns into a classical bit that houses only a single value.

D-Wave claims to have a found a solution to the decoherence problem and that appears to be borne out by the USC researchers. Still, it isn’t a general quantum computer (from Wetz’s article),

… researchers at USC say that the system appears to display a phenomenon called “quantum annealing” that suggests it’s truly operating in the quantum realm. Regardless, the D-Wave is not a general quantum computer—that is, it’s not a computer for just any task. But D-Wave says the machine is well-suited to “optimization” problems, where you’re facing many, many different ways forward and must pick the best option, and to machine learning, where computers teach themselves tasks by analyzing large amount of data.

It takes a lot of innovation before you make big strides forward and I think D-Wave is to be congratulated on producing what is to my knowledge the only commercially available form of quantum computing of any sort in the world.

ETA Oct. 6, 2015* at 1230 hours PST: Minutes after publishing about D-Wave I came across this item (h/t Quirks & Quarks twitter) about Australian researchers and their quantum computing breakthrough. From an Oct. 6, 2015 article by Hannah Francis for the Sydney (Australia) Morning Herald,

For decades scientists have been trying to turn quantum computing — which allows for multiple calculations to happen at once, making it immeasurably faster than standard computing — into a practical reality rather than a moonshot theory. Until now, they have largely relied on “exotic” materials to construct quantum computers, making them unsuitable for commercial production.

But researchers at the University of New South Wales have patented a new design, published in the scientific journal Nature on Tuesday, created specifically with computer industry manufacturing standards in mind and using affordable silicon, which is found in regular computer chips like those we use every day in smartphones or tablets.

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“Our team at UNSW has just cleared a major hurdle to making quantum computing a reality,” the director of the university’s Australian National Fabrication Facility, Andrew Dzurak, the project’s leader, said.

“As well as demonstrating the first quantum logic gate in silicon, we’ve also designed and patented a way to scale this technology to millions of qubits using standard industrial manufacturing techniques to build the world’s first quantum processor chip.”

According to the article, the university is looking for industrial partners to help them exploit this breakthrough. Fisher’s article features an embedded video, as well as, more detail.

*It was Oct. 6, 2015 in Australia but Oct. 5, 2015 my side of the international date line.

ETA Oct. 6, 2015 (my side of the international date line): An Oct. 5, 2015 University of New South Wales news release on EurekAlert provides additional details.

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

A two-qubit logic gate in silicon by M. Veldhorst, C. H. Yang, J. C. C. Hwang, W. Huang,    J. P. Dehollain, J. T. Muhonen, S. Simmons, A. Laucht, F. E. Hudson, K. M. Itoh, A. Morello    & A. S. Dzurak. Nature (2015 doi:10.1038/nature15263 Published online 05 October 2015

This paper is behind a paywall.

Superposition in biological processes

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Applying the concept of superposition to photosynthesis and olfaction is not the first thought that would have occurred to me on stumbling across the European Union’s PAPETS project (Phonon-Assisted Processes for Energy Transfer and Sensing). Thankfully, a July 9, 2015 news item on Nanowerk sets the record straight (Note: A link has been removed),

Quantum physics is helping researchers to better understand photosynthesis and olfaction.

Can something be for instance in two different places at the same time? According to quantum physics, it can. More precisely, in line with the principle of ‘superposition’, a particle can be described as being in two different states simultaneously.

While it may sound like voodoo to the non-expert, superposition is based on solid science. Researchers in the PAPETS project are exploring this and other phenomena on the frontier between biology and quantum physics. Their goal is to determine the role of vibrational dynamics in photosynthesis and olfaction.

A July 7, 2015 research news article on the CORDIS website, which originated the news item, further explains (Note: A link has been removed),

Quantum effects in a biological system, namely in a photosynthetic complex, were first observed by Greg Engel and collaborators in 2007, in the USA. These effects were reproduced in different laboratories at a temperature of around -193 degrees Celsius and subsequently at ambient temperature.

‘What’s surprising and exciting is that these quantum effects have been observed in biological complexes, which are large, wet and noisy systems,’ says PAPETS project coordinator, Dr. Yasser Omar, researcher at Instituto de Telecomunicações and professor at Universidade de Lisboa [Portugal]. ‘Superposition is fragile and we would expect it to be destroyed by the environment.’

Superposition contributes to more efficient energy transport. An exciton, a quantum quasi-particle carrying energy, can travel faster along the photosynthetic complex due to the fact that it can exist in two states simultaneously. When it comes to a bifurcation it need not choose left or right. It can proceed down both paths simultaneously.

‘It’s like a maze,’ says Dr. Omar. ‘Only one door leads to the exit but the exciton can probe both left and right at the same time. It’s more efficient.’

Dr. Omar and his colleagues believe that a confluence of factors help superposition to be effected and maintained, namely the dynamics of the vibrating environment, whose role is precisely what the PAPETS project aims to understand and exploit.

Theory and experimentation meet

The theories being explored by PAPETS are also tested in experiments to validate them and gain further insights. To study quantum transport in photosynthesis, for example, researchers shoot fast laser pulses into biological systems. They then observe interference along the transport network, a signature of wavelike phenomena.

‘It’s like dropping stones into a lake,’ explains Dr. Omar. ‘You can then see whether the waves that are generated grow bigger or cancel each other when they meet.’

Applications: more efficient solar cells and odour detection

While PAPETS is essentially an exploratory project, it is generating insights that could have practical applications. PAPETS’ researchers are getting a more fundamental understanding of how photosynthesis works and this could result in the design of much more efficient solar cells.

Olfaction, the capacity to recognise and distinguish different odours, is another promising area. Experiments focus on the behaviour of Drosophila flies. So far, researchers suspect that the tunnelling of electrons associated to the internal vibrations of a molecule may be a signature of odour. Dr. Omar likens this tunnelling to a ping-pong ball resting in a bowl that goes through the side of the bowl to appear outside it.

This work could have applications in the food, water, cosmetics or drugs industries. Better artificial odour sensing could be used to detect impurities or pollution, for example.

‘Unlike seeing, hearing or touching, the sense of smell is difficult to reproduce artificially with high efficacy,’ says Dr. Omar.

The PAPETS project, involving 7 partners, runs from September 2014 to August 2016 and has a budgeted EU contribution funding of EUR 1.8 million.

You can find out more about PAPETS here. In the meantime, I found the other partners in the project (in addition to Portugal), from the PAPETS Partners webpage (Note: Links have been removed),

– Controlled Quantum Dynamics Group, Universität Ulm (UULM), Germany. PI: Martin Plenio and Susana Huelga.
– Biophysics Research Group, Vrije Universiteit Amsterdam (VUA), Netherlands. PI: Rienk van Grondelle and Roberta Croce.
– Department of Chemical Sciences, Università degli Studi di Padova (UNIPD), Italy. PI: Elisabetta Collini.
– Biomedical Sciences Research Centre “Alexander Fleming” (FLEMING), Athens, Greece. PI: Luca Turin and Efthimios M. Skoulakis.
– Biological Physics and Complex Systems Group, Centre National de la Recherche Scientifique (CNRS), Orléans, France. PI: Francesco Piazza.
– Quantum Physics of Biomolecular Processes, University College London (UCL), UK. PI: Alexandra Olaya-Castro.

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

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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.

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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.

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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.

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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.