When it comes to studying transportation systems, stock markets and the weather, quantum mechanics is probably the last thing to come to mind.
However, scientists at Australia’s Griffith University and Singapore’s Nanyang Technological University have just performed a ‘proof of principle’ experiment showing that when it comes to simulating such complex processes in the macroscopic world quantum mechanics can provide an unexpected advantage.
Griffith’s Professor Geoff Pryde, who led the project, says that such processes could be simulated using a “quantum hard drive”, much smaller than the memory required for conventional simulations.
“Stephen Hawking once stated that the 21st century is the ‘century of complexity’, as many of today’s most pressing problems, such as understanding climate change or designing transportation system, involve huge networks of interacting components,” he says.
“Their simulation is thus immensely challenging, requiring storage of unprecedented amounts of data. What our experiments demonstrate is a solution may come from quantum theory, by encoding this data into a quantum system, such as the quantum states of light.”
Einstein once said that “God does not play dice with the universe,” voicing his disdain with the idea that quantum particles contain intrinsic randomness.
“But theoretical studies showed that this intrinsic randomness is just the right ingredient needed to reduce the memory cost for modelling partially random statistics,” says Dr Mile Gu, a member of the team who developed the initial theory.
In contrast with the usual binary storage system – the zeroes and ones of bits – quantum bits can be simultaneously 0 and 1, a phenomenon known as quantum superposition.
The researchers, in their paper published in Science Advances, say this freedom allows quantum computers to store many different states of the system being simulated in different superpositions, using less memory overall than in a classical computer.
The team constructed a proof-of-principle quantum simulator using a photon – a single particle of light – interacting with another photon.
The data showed that the quantum system could complete the task with much less information stored than the classical computer– a factor of 20 improvements at the best point.
“Although the system was very small – even the ordinary simulation required only a single bit of memory – it proved that quantum advantages can be achieved,” Pryde says.
“Theoretically, large improvements can also be realised for much more complex simulations, and one of the goals of this research program is to advance the demonstrations to more complex problems.”
Collaboration between quantum scientists and City of Calgary sets a distance record for teleporting a photon state over a fibre network
What if you could behave like the crew on the Starship Enterprise and teleport yourself home or anywhere else in the world? As a human, you’re probably not going to realize this any time soon; if you’re a photon, you might want to keep reading.
Through a collaboration between the University of Calgary, The City of Calgary and researchers in the United States, a group of physicists led by Wolfgang Tittel, professor in the Department of Physics and Astronomy at the University of Calgary have successfully demonstrated teleportation of a photon (an elementary particle of light) over a straight-line distance of six kilometres using The City of Calgary’s fibre optic cable infrastructure. The project began with an Urban Alliance seed grant in 2014.
This accomplishment, which set a new record for distance of transferring a quantum state by teleportation, has landed the researchers a spot in the prestigious Nature Photonics scientific journal. The finding was published back-to-back with a similar demonstration by a group of Chinese researchers. Read the article, “Quantum Teleportation Across a Metropolitan Fiber Network.”
“Such a network will enable secure communication without having to worry about eavesdropping, and allow distant quantum computers to connect,” says Tittel.
Experiment draws on ‘spooky action at a distance’
The experiment is based on the entanglement property of quantum mechanics, also known as “spooky action at a distance” — a property so mysterious that not even Einstein could come to terms with it.
“Being entangled means that the two photons that form an entangled pair have properties that are linked regardless of how far the two are separated,” explains Tittel. “When one of the photons was sent over to City Hall, it remained entangled with the photon that stayed at the University of Calgary.”
Next, the photon whose state was teleported to the university was generated in a third location in Calgary and then also travelled to City Hall where it met the photon that was part of the entangled pair.
“What happened is the disembodied transfer of the photon’s quantum state onto the remaining photon of the entangled pair, which is the one that remained six kilometres away at the university,” says Tittel.
City’s accessible dark fibre makes research possible
The research could not be possible without access to the proper technology. One of the critical pieces of infrastructure that support quantum networking is accessible dark fibre. Dark fibre, so named because of its composition — a single optical cable with no electronics or network equipment on the alignment — doesn’t interfere with quantum technology.
The City of Calgary is building and provisioning dark fibre to enable next-generation municipal services today and for the future.
“By opening The City’s dark fibre infrastructure to the private and public sector, non-profit companies, and academia, we help enable the development of projects like quantum encryption and create opportunities for further research, innovation and economic growth in Calgary,” said Tyler Andruschak, project manager with Innovation and Collaboration at The City of Calgary.
“The university receives secure access to a small portion of our fibre optic infrastructure and The City may benefit in the future by leveraging the secure encryption keys generated out of the lab’s research to protect our critical infrastructure,” said Andruschak. In order to deliver next-generation services to Calgarians, The City has been increasing its fibre optic footprint, connecting all City buildings, facilities and assets.
Timed to within one millionth of one millionth of a second
As if teleporting a photon wasn’t challenging enough, Tittel and his team encountered a number of other roadblocks along the way.
Due to changes in the outdoor temperature, the transmission time of photons from their creation point to City Hall varied over the course of a day — the time it took the researchers to gather sufficient data to support their claim. This change meant that the two photons would not meet at City Hall.
“The challenge was to keep the photons’ arrival time synchronized to within 10 pico-seconds,” says Tittel. “That is one trillionth, or one millionth of one millionth of a second.”
Secondly, parts of their lab had to be moved to two locations in the city, which as Tittel explains was particularly tricky for the measurement station at City Hall which included state-of-the-art superconducting single-photon detectors developed by the National Institute for Standards and Technology, and NASA’s Jet Propulsion Laboratory.
“Since these detectors only work at temperatures less than one degree above absolute zero the equipment also included a compact cryostat,” said Tittel.
Milestone towards a global quantum Internet
This demonstration is arguably one of the most striking manifestations of a puzzling prediction of quantum mechanics, but it also opens the path to building a future quantum internet, the long-term goal of the Tittel group.
Researchers have levitated a tiny nanodiamond particle with a laser in a vacuum chamber, using the technique for the first time to detect and measure its “torsional vibration,” an advance that could bring new types of sensors and studies in quantum mechanics.
The experiment represents a nanoscale version of the torsion balance used in the classic Cavendish experiment, performed in 1798 by British scientist Henry Cavendish, which determined Newton’s gravitational constant. A bar balancing two lead spheres at either end was suspended on a thin metal wire. Gravity acting on the two weights caused the wire and bar to twist, and this twisting – or torsion – was measured to calculate the gravitational force.
In the new experiment, an oblong-shaped nanodiamond levitated by a laser beam in a vacuum chamber served the same role as the bar, and the laser beam served the same role as the wire in Cavendish’s experiment.
“A change of the orientation of the nanodiamond caused the polarization of the laser beam to twist,” said Tongcang Li, an assistant professor of physics and astronomy and electrical and computer engineering at Purdue University. “Torsion balances have played historic roles in the development of modern physics. Now, an optically levitated ellipsoidal nanodiamond in a vacuum provides a new nanoscale torsion balance that will be many times more sensitive.”
Findings are detailed in a paper that appeared on Thursday (Sept. 15) in the journal Physical Review Letters.
“This is the first experimental observation of torsional motion of a nanoparticle levitated in a vacuum and represents a very sensitive torque detector,” Li said. “In principle, we could detect the torque on a single electron or a single proton.”
The paper was authored by Purdue postdoctoral research associate Thai M. Hoang; student Yue Ma from Tsinghua University in China; Purdue graduate students Jonghoon Ahn and Jaehoon Bang;Francis Robicheaux, a Purdue professor of physics and astronomy; Zhang-Qi Yin, an assistant research fellow at Tsinghua University; and Li.
The paper details the detection of torsional vibration, a proposal to use the technique for torque sensing and also to achieve torsional “ground state cooling,” which could aid efforts to study quantum theory and realize potential applications in quantum information processing and high-precision measurement for sensors.
This cooling reduces “noise” caused by vibrating molecules and atoms, making it possible to precisely measure torque and probe the relationships between motion and electron “spin.” Electrons can be thought of as having two distinct spin states, “up” or “down,” and this phenomenon might be used in future quantum simulations.
The paper includes experimental and theoretical portions.
“Experimentally, we observed torsional motion, and the theoretical part is a proposal of how to cool down the motion to achieve quantum ground state,” Li said.
The nanodiamonds are about 100 nanometers in diameter, or roughly the size of a virus. Future research will include efforts to achieve ground state cooling.
Until quite recently, creating a hologram of a single photon was believed to be impossible due to fundamental laws of physics. However, scientists at the Faculty of Physics, University of Warsaw, have successfully applied concepts of classical holography to the world of quantum phenomena. A new measurement technique has enabled them to register the first ever hologram of a single light particle, thereby shedding new light on the foundations of quantum mechanics.
Scientists at the Faculty of Physics, University of Warsaw, have created the first ever hologram of a single light particle. The spectacular experiment, reported in the prestigious journal Nature Photonics, was conducted by Dr. Radoslaw Chrapkiewicz and Michal Jachura under the supervision of Dr. Wojciech Wasilewski and Prof. Konrad Banaszek. Their successful registering of the hologram of a single photon heralds a new era in holography: quantum holography, which promises to offer a whole new perspective on quantum phenomena.
“We performed a relatively simple experiment to measure and view something incredibly difficult to observe: the shape of wavefronts of a single photon,” says Dr. Chrapkiewicz.
Using a computer game, a research group at Aarhus University has found a way to gain deeper insight into the human thought process.
The results have amazed the research director, who has discovered a kind of ‘atlas of thoughts’. And that is not all. The group can also reveal which gender is best at solving quantum problems.
Are humans born with the ability to solve problems or is it something we learn along the way? A research group at the Department of Physics and Astronomy, Aarhus University, is working to find answers to this question.
The research group has developed a computer game called Quantum Moves, which has been played 400,000 times by ordinary people. This has provided unique and deep insight into the human brain’s ability to solve problems. The game involves moving atoms around on the screen and scoring points by finding the best way to do so.
In this way, ordinary people contribute to quantum physics research. Associate Professor Jacob Sherson, director of the research group, explains that a player’s ability to make a strategy and solve a problem is markedly different from the way a computer works. Based on 400,000 game solutions, he can make a start on compiling the results.