Nanotechnology Now

Our NanoNews Digest Sponsors


Heifer International

Wikipedia Affiliate Button


DHgate

Home > Press > Watching Schrödinger's cat die (or come to life): Steering quantum evolution & using probes to conduct continuous error correction in quantum computers

Continuous monitoring of a quantum system can direct the quantum state along a random path. This three-dimensional map shows how scientists tracked the transition between two qubit states many times to determine the optimal path.

Credit: Irfan Siddiqi, UC Berkeley
Continuous monitoring of a quantum system can direct the quantum state along a random path. This three-dimensional map shows how scientists tracked the transition between two qubit states many times to determine the optimal path.

Credit: Irfan Siddiqi, UC Berkeley

Abstract:
One of the famous examples of the weirdness of quantum mechanics is the paradox of Schrödinger's cat.

If you put a cat inside an opaque box and make his life dependent on a random event, when does the cat die? When the random event occurs, or when you open the box?

Watching Schrödinger's cat die (or come to life): Steering quantum evolution & using probes to conduct continuous error correction in quantum computers

Berkeley, CA | Posted on July 30th, 2014

Though common sense suggests the former, quantum mechanics - or at least the most common "Copenhagen" interpretation enunciated by Danish physicist Neils Bohr in the 1920s - says it's the latter. Someone has to observe the result before it becomes final. Until then, paradoxically, the cat is both dead and alive at the same time.

University of California, Berkeley, physicists have for the first time showed that, in fact, it's possible to follow the metaphorical cat through the whole process, whether he lives or dies in the end.

"Gently recording the cat's paw prints both makes it die, or come to life, as the case may be, and allows us to reconstruct its life history," said Irfan Siddiqi, UC Berkeley associate professor of physics, who is senior author of a cover article describing the result in the July 31 issue of the journal Nature.

The Schrödinger's cat paradox is a critical issue in quantum computers, where the input is an entanglement of states - like the cat's entangled life and death- yet the answer to whether the animal is dead or alive has to be definite.

"To Bohr and others, the process was instantaneous - when you opened the box, the entangled system collapsed into a definite, classical state. This postulate stirred debate in quantum mechanics," Siddiqi said. "But real-time tracking of a quantum system shows that it's a continuous process, and that we can constantly extract information from the system as it goes from quantum to classical. This level of detail was never considered accessible by the original founders of quantum theory."

For quantum computers, this would allow continuous error correction. The real world, everything from light and heat to vibration, can knock a quantum system out of its quantum state into a real-world, so-called classical state, like opening the box to look at the cat and forcing it to be either dead or alive. A big question regarding quantum computers, Siddiqi said, is whether you can extract information without destroying the quantum system entirely.

"This gets around that fundamental problem in a very natural way," he said. "We can continuously probe a system very gently to get a little bit of information and continuously correct it, nudging it back into line, toward the ultimate goal."

Being two opposing things at the same time

In the world of quantum physics, a system can be in two superposed states at the same time, as long as no one is observing. An observation perturbs the system and forces it into one or the other. Physicists say that the original entangled wave functions collapsed into a classical state.

In the past 10 years, theorists such as Andrew N. Jordan, professor of physics at the University of Rochester and coauthor of the Nature paper, have developed theories predicting the most likely way in which a quantum system will collapse.

"The Rochester team developed new mathematics to predict the most likely path with high accuracy, in the same way one would use Newtown's equations to predict the least cumbersome path of a ball rolling down a mountain," Siddiqi said. "The implications are significant, as now we can design control sequences to steer a system along a certain trajectory. For example, in chemistry one could use this to prefer certain products of a reaction over others."

Lead researcher Steve Weber, a graduate student in Siddiqi's group, and Siddiqi's former postdoctoral fellow Kater Murch, now an assistant professor of physics at Washington University in St. Louis, proved Jordan correct. They measured the trajectory of the wave function of a quantum circuit - a qubit, analogous to the bit in a normal computer - as it changed. The circuit, a superconducting pendulum, could be in two different energy states and was coupled to a second circuit to read out the final voltage, corresponding to the pendulum's frequency.

"If you did this experiment many, many times, measuring the road the system took each time and the states it went through, we could determine what the most likely path is," Siddiqi said. "Then we could design a control sequence to take the road we want to take for a given quantum evolution."

If you probed a chemical reaction in detail, for example, you could find the most likely path the reaction would take and design a way to steer the reaction to the products you want, not the most likely, Siddiqi said.

"The experiment demonstrates that, for any choice of final quantum state, the most likely or 'optimal path' connecting them in a given time can be found and predicted," Jordan said. "This verifies the theory and opens the way for active quantum control techniques."

###

The work was supported in part by the Office of Naval Research and the Office of the Director of National Intelligence (ODNI) of the Intelligence Advanced Research Projects Activity (IARPA), through the Army Research Office.

####

For more information, please click here

Contacts:
Robert Sanders

510-643-6998

Copyright © University of California - Berkeley

If you have a comment, please Contact us.

Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

Bookmark:
Delicious Digg Newsvine Google Yahoo Reddit Magnoliacom Furl Facebook

Related News Press

News and information

Simple attraction: Researchers control protein release from nanoparticles without encapsulation: U of T Engineering discovery stands to improve reliability and fabrication process for treatments to conditions such as spinal cord damage and stroke May 28th, 2016

Scientists illuminate a hidden regulator in gene transcription: New super-resolution technique visualizes important role of short-lived enzyme clusters May 27th, 2016

Doubling down on Schrödinger's cat May 27th, 2016

Deep Space Industries and SFL selected to provide satellites for HawkEye 360’s Pathfinder mission: The privately-funded space-based global wireless signal monitoring system will be developed by Deep Space Industries and UTIAS Space Flight Laboratory May 26th, 2016

Physics

Doubling down on Schrödinger's cat May 27th, 2016

Thermal modification of wood and a complex study of its properties by magnetic resonance May 26th, 2016

Govt.-Legislation/Regulation/Funding/Policy

Scientists illuminate a hidden regulator in gene transcription: New super-resolution technique visualizes important role of short-lived enzyme clusters May 27th, 2016

Doubling down on Schrödinger's cat May 27th, 2016

Harnessing solar and wind energy in one device could power the 'Internet of Things' May 26th, 2016

Thermal modification of wood and a complex study of its properties by magnetic resonance May 26th, 2016

Quantum Computing

Doubling down on Schrödinger's cat May 27th, 2016

Dartmouth team creates new method to control quantum systems May 24th, 2016

Theorists smooth the way to modeling quantum friction: New paradigm offers a strategy for solving one of quantum mechanics' oldest problems May 18th, 2016

Scientists take a major leap toward a 'perfect' quantum metamaterial: Berkeley Lab, UC Berkeley researchers lead study that uses trapped atoms in an artificial crystal of light May 13th, 2016

Discoveries

Simple attraction: Researchers control protein release from nanoparticles without encapsulation: U of T Engineering discovery stands to improve reliability and fabrication process for treatments to conditions such as spinal cord damage and stroke May 28th, 2016

Scientists illuminate a hidden regulator in gene transcription: New super-resolution technique visualizes important role of short-lived enzyme clusters May 27th, 2016

Doubling down on Schrödinger's cat May 27th, 2016

Finding a new formula for concrete: Researchers look to bones and shells as blueprints for stronger, more durable concrete May 26th, 2016

Announcements

Simple attraction: Researchers control protein release from nanoparticles without encapsulation: U of T Engineering discovery stands to improve reliability and fabrication process for treatments to conditions such as spinal cord damage and stroke May 28th, 2016

Scientists illuminate a hidden regulator in gene transcription: New super-resolution technique visualizes important role of short-lived enzyme clusters May 27th, 2016

Doubling down on Schrödinger's cat May 27th, 2016

Deep Space Industries and SFL selected to provide satellites for HawkEye 360’s Pathfinder mission: The privately-funded space-based global wireless signal monitoring system will be developed by Deep Space Industries and UTIAS Space Flight Laboratory May 26th, 2016

Interviews/Book Reviews/Essays/Reports/Podcasts/Journals/White papers

Simple attraction: Researchers control protein release from nanoparticles without encapsulation: U of T Engineering discovery stands to improve reliability and fabrication process for treatments to conditions such as spinal cord damage and stroke May 28th, 2016

Scientists illuminate a hidden regulator in gene transcription: New super-resolution technique visualizes important role of short-lived enzyme clusters May 27th, 2016

Doubling down on Schrödinger's cat May 27th, 2016

Finding a new formula for concrete: Researchers look to bones and shells as blueprints for stronger, more durable concrete May 26th, 2016

Homeland Security

Team builds first quantum cascade laser on silicon: Eliminates the need for an external light source for mid-infrared silicon photonic devices or photonic circuits April 21st, 2016

Nanoporous material's strange "breathing" behavior April 7th, 2016

Sniffing out a dangerous vapor: University of Utah engineers develop material that can sense fuel leaks and fuel-based explosives March 28th, 2016

Detecting and identifying explosives with single test December 10th, 2015

Military

Doubling down on Schrödinger's cat May 27th, 2016

Nanoscale Trojan horses treat inflammation May 24th, 2016

Programmable materials find strength in molecular repetition May 23rd, 2016

Rice de-icer gains anti-icing properties: Dual-function, graphene-based material good for aircraft, extreme environments May 23rd, 2016

NanoNews-Digest
The latest news from around the world, FREE




  Premium Products
NanoNews-Custom
Only the news you want to read!
 Learn More
NanoTech-Transfer
University Technology Transfer & Patents
 Learn More
NanoStrategies
Full-service, expert consulting
 Learn More











ASP
Nanotechnology Now Featured Books




NNN

The Hunger Project







Car Brands
Buy website traffic