Tag Archives: Robert Fickler

For first time: high-dimensional quantum encryption performed in real world city conditions

Having congratulated China on the world’s first quantum communication network a few weeks ago (August 22, 2017 posting), this quantum encryption story seems timely. From an August 24, 2017 news item on phys.org,

For the first time, researchers have sent a quantum-secured message containing more than one bit of information per photon through the air above a city. The demonstration showed that it could one day be practical to use high-capacity, free-space quantum communication to create a highly secure link between ground-based networks and satellites, a requirement for creating a global quantum encryption network.

Quantum encryption uses photons to encode information in the form of quantum bits. In its simplest form, known as 2D encryption, each photon encodes one bit: either a one or a zero. Scientists have shown that a single photon can encode even more information—a concept known as high-dimensional quantum encryption—but until now this has never been demonstrated with free-space optical communication in real-world conditions. With eight bits necessary to encode just one letter, for example, packing more information into each photon would significantly speed up data transmission.

This looks like donuts on a stick to me,

For the first time, researchers have demonstrated sending messages in a secure manner using high dimensional quantum cryptography in realistic city conditions. Image Credit: SQO team, University of Ottawa.

An Aug. 24, 2017 Optical Society news release (also on EurekAlert), which originated the news item, describes the work done by a team in Ottawa, Canada, (Note: The ‘Congratulate China’ piece (August 22, 2017 posting) includes excerpts from an article that gave a brief survey of various national teams [including Canada] working on quantum communication networks; Links have been removed),

“Our work is the first to send messages in a secure manner using high-dimensional quantum encryption in realistic city conditions, including turbulence,” said research team lead, Ebrahim Karimi, University of Ottawa, Canada. “The secure, free-space communication scheme we demonstrated could potentially link Earth with satellites, securely connect places where it is too expensive to install fiber, or be used for encrypted communication with a moving object, such as an airplane.”

For the first time, researchers have demonstrated sending messages in a secure manner using high dimensional quantum cryptography in realistic city conditions. Image Credit: SQO team, University of Ottawa.

As detailed in Optica, The Optical Society’s journal for high impact research, the researchers demonstrated 4D quantum encryption over a free-space optical network spanning two buildings 0.3 kilometers apart at the University of Ottawa. This high-dimensional encryption scheme is referred to as 4D because each photon encodes two bits of information, which provides the four possibilities of 01, 10, 00 or 11.

In addition to sending more information per photon, high-dimensional quantum encryption can also tolerate more signal-obscuring noise before the transmission becomes unsecure. Noise can arise from turbulent air, failed electronics, detectors that don’t work properly and from attempts to intercept the data. “This higher noise threshold means that when 2D quantum encryption fails, you can try to implement 4D because it, in principle, is more secure and more noise resistant,” said Karimi.

Using light for encryption

Today, mathematical algorithms are used to encrypt text messages, banking transactions and health information. Intercepting these encrypted messages requires figuring out the exact algorithm used to encrypt a given piece of data, a feat that is difficult now but that is expected to become easier in the next decade or so as computers become more powerful.

Given the expectation that current algorithms may not work as well in the future, more attention is being given to stronger encryption techniques such as quantum key distribution, which uses properties of light particles known as quantum states to encode and send the key needed to decrypt encoded data.

Although wired and free-space quantum encryption has been deployed on some small, local networks, implementing it globally will require sending encrypted messages between ground-based stations and the satellite-based quantum communication networks that would link cities and countries. Horizontal tests through the air can be used to simulate sending signals to satellites, with about three horizontal kilometers being roughly equal to sending the signal through the Earth’s atmosphere to a satellite.

Before trying a three-kilometer test, the researchers wanted to see if it was even possible to perform 4D quantum encryption outside. This was thought to be so challenging that some other scientists in the field said that the experiment would not work. One of the primary problems faced during any free-space experiment is dealing with air turbulence, which distorts the optical signal.

Real-world testing

For the tests, the researchers brought their laboratory optical setups to two different rooftops and covered them with wooden boxes to provide some protection from the elements. After much trial and error, they successfully sent messages secured with 4D quantum encryption over their intracity link. The messages exhibited an error rate of 11 percent, below the 19 percent threshold needed to maintain a secure connection. They also compared 4D encryption with 2D, finding that, after error correction, they could transmit 1.6 times more information per photon with 4D quantum encryption, even with turbulence.

“After bringing equipment that would normally be used in a clean, isolated lab environment to a rooftop that is exposed to the elements and has no vibration isolation, it was very rewarding to see results showing that we could transmit secure data,” said Alicia Sit, an undergraduate student in Karimi’s lab.

As a next step, the researchers are planning to implement their scheme into a network that includes three links that are about 5.6 kilometers apart and that uses a technology known as adaptive optics to compensate for the turbulence. Eventually, they want to link this network to one that exists now in the city. “Our long-term goal is to implement a quantum communication network with multiple links but using more than four dimensions while trying to get around the turbulence,” said Sit.

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

High-dimensional intracity quantum cryptography with structured photons by Alicia Sit, Frédéric Bouchard, Robert Fickler, Jérémie Gagnon-Bischoff, Hugo Larocque, Khabat Heshami, Dominique Elser, Christian Peuntinger, Kevin Günthner, Bettina Heim, Christoph Marquardt, Gerd Leuchs, Robert W. Boyd, and Ebrahim Karimi. Optica Vol. 4, Issue 9, pp. 1006-1010 (2017) •https://doi.org/10.1364/OPTICA.4.001006

This is an open access paper.

Quantum physics experiments designed by an algorithm

A Feb. 22, 2016 news item on Nanotechnology Now describes research into quantum physics performed by an algorithm,

Quantum physicist Mario Krenn and his colleagues in the group of Anton Zeilinger from the Faculty of Physics at the University of Vienna and the Austrian Academy of Sciences have developed an algorithm which designs new useful quantum experiments. As the computer does not rely on human intuition, it finds novel unfamiliar solutions.

The researchers have provided an image illustrating their work,

Caption: The algorithm Melvin found out that the most simple realization can be asymmetric and therefore counterintuitive. Credit: Copyright: Robert Fickler, Universität Wien (University of Vienna)

Caption: The algorithm Melvin found out that the most simple realization can be asymmetric and therefore counterintuitive. Credit: Copyright: Robert Fickler, Universität Wien (University of Vienna)

A Feb. 22, 2016 University of Vienna press release (also on EurekAlert), which originated the news item, expands on the theme,

The idea was developed when the physicists wanted to create new quantum states in the laboratory, but were unable to conceive of methods to do so. “After many unsuccessful attempts to come up with an experimental implementation, we came to the conclusion that our intuition about these phenomena seems to be wrong. We realized that in the end we were just trying random arrangements of quantum building blocks. And that is what a computer can do as well – but thousands of times faster”, explains Mario Krenn, PhD student in Anton Zeilinger’s group and first author research.

After a few hours of calculation, their algorithm – which they call Melvin – found the recipe to the question they were unable to solve, and its structure surprised them. Zeilinger says: “Suppose I want build an experiment realizing a specific quantum state I am interested in. Then humans intuitively consider setups reflecting the symmetries of the state. Yet Melvin found out that the most simple realization can be asymmetric and therefore counterintuitive. A human would probably never come up with that solution.”

The physicists applied the idea to several other questions and got dozens of new and surprising answers. “The solutions are difficult to understand, but we were able to extract some new experimental tricks we have not thought of before. Some of these computer-designed experiments are being built at the moment in our laboratories”, says Krenn.

Melvin not only tries random arrangements of experimental components, but also learns from previous successful attempts, which significantly speeds up the discovery rate for more complex solutions. In the future, the authors want to apply their algorithm to even more general questions in quantum physics, and hope it helps to investigate new phenomena in laboratories.

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

Automated Search for new Quantum Experiments by Mario Krenn, Mehul Malik, Robert Fickler, Radek Lapkiewicz, Anton Zeilinger. arXiv (Submitted on 9 Sep 2015 (v1), last revised 20 Feb 2016 (this version, v2))

The version of the paper on arXiv.org is open access. The paper has also been accepted by Physical Review Letters but does not seem to have been published online or in print yet,

Automated search for new quantum experiments
by Mario Krenn, Mehul Malik, Robert Fickler, Radek Lapkiewicz, and Anton Zeilinger. Phys. Rev. Lett. Accepted 27 January 2016

There is a copy of the abstract available on the Physical Review Letters site.

Seeing quantum entanglement and using quantum entanglement to build a wormhole

Kudos to the team from the Vienna Center for Quantum Science and Technology for the great musical accompaniment on their video showing quantum entanglement in real time,

A Dec. 4, 2013 news item on Nanowerk provides more details,

Einstein called quantum entanglement “spooky action at a distance”. Now, a team from the Vienna Center for Quantum Science and Technology has reported imaging of entanglement events where the influence of the measurement of one particle on its distant partner particle is directly visible (“Real-Time Imaging of Quantum Entanglement”).

The Dec. 4, 2013 Andor news release, which originated the news item, gives more details about the team’s work and about the Andor camera which enabled it,

The key to their success is the Andor iStar 334T Intensified CCD (ICCD) camera, which is capable of very fast (nanosecond) and precise (picosecond) optical gating speeds. Unlike the relatively long microsecond exposure times of CCD and EMCCD cameras which inhibits their usefulness in ultra-high-speed imaging, this supreme level of temporal resolution made it possible for the team to perform a real-time coincidence imaging of entanglement for the first time.

“The Andor iStar ICCD camera is fast enough, and sensitive enough, to image in real-time the effect of the measurement of one photon on its entangled partner,” says Robert Fickler of the Institute for Quantum Optics and Quantum Information. “Using ICCD cameras to evaluate the number of photons from a registered intensity within a given region opens up new experimental possibilities to determine more efficiently the structure and properties of spatial modes from only single intensity images. Our results suggest that triggered ICCD cameras will advance quantum optics and quantum information experiments where complex structures of single photons need to be investigated with high spatio-temporal resolution.”

According to Antoine Varagnat, Product Specialist at Andor, “The experiment produces pairs of photons which are entangled so as to have opposite polarisations. For instance, if one of a pair has horizontal polarisation, the other has vertical, and so on. The first photon is sent to polarising glass that transmits photons of one angle only, followed by a detector to register photons which make it through the glass. The other photon is delayed by a fibre, then its entangled property is coherently transferred from the polarisation to the spatial mode and afterwards brought to the high-speed, ultra-sensitive iStar camera.

“The use of the ICCD camera allowed the team to demonstrate the high flexibility of the setup in creating any desired spatial-mode entanglement. Their results suggest that visual imaging in quantum optics not only provides a better intuitive understanding of entanglement but will also improve applications of quantum science,” concludes Varagnat.

Research into quantum entanglement was instigated in 1935 by Albert Einstein, Boris Podolsky and Nathan Rosen, in a paper critiquing quantum mechanics. Erwin Schrödinger also wrote several papers shortly afterwards. Although these first studies focused on the counterintuitive properties of entanglement with the aim of criticising quantum mechanics, entanglement was eventually verified experimentally and recognised as a valid, fundamental feature of quantum mechanics. Nowadays, the focus of the research has changed to its utilization in communications and computation, and has been used to realise quantum teleportation experimentally.

The team’s work is chronicled in this study,

Real-Time Imaging of Quantum Entanglement by Robert Fickler, Mario Krenn, Radek Lapkiewicz, Sven Ramelow & Anton Zeilinger. Scientific Reports 3, Article number: 1914 doi:10.1038/srep01914 Published 29 May 2013

This is an open access paper.

Meanwhile, researchers at the University of Washington (Seattle, Washington state) explore the quantum entanglement phenomenon with an eye to wormholes (from the De.c 3, 2013 University of Washington news release [also on EurekAlter]),

Quantum entanglement, a perplexing phenomenon of quantum mechanics that Albert Einstein once referred to as “spooky action at a distance,” could be even spookier than Einstein perceived.

Physicists at the University of Washington and Stony Brook University in New York believe the phenomenon might be intrinsically linked with wormholes, hypothetical features of space-time that in popular science fiction can provide a much-faster-than-light shortcut from one part of the universe to another.

But here’s the catch: One couldn’t actually travel, or even communicate, through these wormholes, said Andreas Karch, a UW physics professor.

Quantum entanglement occurs when a pair or a group of particles interact in ways that dictate that each particle’s behavior is relative to the behavior of the others. In a pair of entangled particles, if one particle is observed to have a specific spin, for example, the other particle observed at the same time will have the opposite spin.

The “spooky” part is that, as research has confirmed, the relationship holds true no matter how far apart the particles are – across the room or across several galaxies. If the behavior of one particle changes, the behavior of both entangled particles changes simultaneously, no matter how far away they are.

Recent research indicated that the characteristics of a wormhole are the same as if two black holes were entangled, then pulled apart. Even if the black holes were on opposite sides of the universe, the wormhole would connect them.

Black holes, which can be as small as a single atom or many times larger than the sun, exist throughout the universe, but their gravitational pull is so strong that not even light can escape from them.

If two black holes were entangled, Karch said, a person outside the opening of one would not be able to see or communicate with someone just outside the opening of the other.

“The way you can communicate with each other is if you jump into your black hole, then the other person must jump into his black hole, and the interior world would be the same,” he said.

The work demonstrates an equivalence between quantum mechanics, which deals with physical phenomena at very tiny scales, and classical geometry – “two different mathematical machineries to go after the same physical process,” Karch said. The result is a tool scientists can use to develop broader understanding of entangled quantum systems.

“We’ve just followed well-established rules people have known for 15 years and asked ourselves, ‘What is the consequence of quantum entanglement?'”

The researchers have provided an illustration, which looks more like a ‘smiley face’ to me. Are wormholes smiley faces in space,

Alan Stonebraker/American Physical Society This illustration demonstrates a wormhole connecting two black holes.

Alan Stonebraker/American Physical Society
This illustration demonstrates a wormhole connecting two black holes.

Here’s a link to and a citation for the research paper on quantum entanglement and wormholes,

Holographic Dual of an Einstein-Podolsky-Rosen Pair has a Wormhole by Kristan Jensen and Andreas Karch. Phys. Rev. Lett. 111, 211602 (2013) [5 pages] Published 20 November 2013

This paper is behind a paywall.

ETA Dec. 11, 2013: There’s a news item today, Dec. 11, 2013, on Nanowerk which casts an interesting light on Andor,

Nanotechnology specialist Oxford Instruments is to take over Belfast-based scientific camera maker Andor in a £176million deal.
The Andor board last night agreed a 525p a share offer, giving a 31 per cent premium over the closing price before Oxford’s initial 500p a share pitch in November.

The two companies have been in talks since July [2013].

Shares in Andor rose 10p to 515p and Oxford Instruments gained 8p to 1566p.

It looks like their Dec. 4, 2013 news release was a leadup to this business news.