Scientists track quantum errors in real time

Jul 14, 2014 by Holly Lauridsen
Scientists track quantum errors in real time
Credit: Shutterstock

(Phys.org) —Scientists at Yale University have demonstrated the ability to track real quantum errors as they occur, a major step in the development of reliable quantum computers. They report their results in the journal Nature.

Quantum computers could significantly improve the computational power of modern computers, but a major problem stands in the way: information loss, or quantum . To combat errors, physicists must be able to detect that an error has occurred and then correct it in , a process known as quantum error correction.

"Ninety-nine percent of will be correcting errors," explained Yale physicist Rob Schoelkopf, Sterling Professor of Applied Physics and Physics. "Demonstrating error correction that actually works is the biggest remaining challenge for building a quantum computer."

Data in standard computers are stored in bits as either 0 or 1, known as classical states. They are largely insensitive to their surroundings. In contrast, quantum computers rely on quantum bits, or qubits, which store data in a third, very fragile state known as a quantum state—a superposition of 0 and 1 simultaneously. Changes in the quibit's environment can force it revert back to one of the classical states of 0 or 1. And when a qubit leaves the quantum state, it also loses the data it was carrying.

In the new research, Schoelkopf's group and other Yale collaborators tackled the first step in quantum error correction—successfully identifying errors as they happen, in their case by means of a reporter atom.

Identifying quantum-computing errors in real time is particularly challenging: Qubits are so fragile that searching for errors can result in more errors. To determine if an error occurred, Schoelkopf and his team relied on an ancilla, or a more stable reporter atom, which detected errors without destroying the state and relayed that information back to the scientists on a computer.

During their experiments, the scientists used a superconducting box containing the ancilla and an unknown number of , or light particles, which were cooled to approximately -459°F, a fraction of a degree above absolute zero. This minimized quantum errors induced by the environment. The team then tracked the photons in the box over time to see if and when the photons escaped. Losing photons from the box indicated lost information, or the occurrence of a quantum error.

The errors need to be detected without learning the exact conditions in the superconducting box, including the number of photons, because determining the conditions in the box can disrupt the qubit quantum state and result in more errors. So the ancilla reported only the photon parity—whether an even or odd number of quantum photons were present in the box—in real time. A change in parity—for example, from even to odd—indicated the loss of a single photon without revealing whether the box had changed from six to five photons or from four to three photons.

The team found success in their first experiment and demonstrated for the first time the tracking of naturally occurring errors, in real time, as would be needed for a real quantum computer.

"We could see errors coming up as they happened," said Yale graduate student and co-author Andrei Petrenko. "We could actually observe on the screen just the kinds of patterns that we were hoping to see."

"This success has given us more confidence to go forward, " said Schoelkopf.

The Yale team is now studying how to fix errors, the second step in and an essential capability for functional quantum computers.

"It is hard to estimate how long it will be until we have functional quantum computers," Schoelkopf said, "but it will be sooner than we think."

Explore further: Physicists correct quantum errors

More information: Tracking photon jumps with repeated quantum non-demolition parity measurements , DOI: 10.1038/nature13436

add to favorites email to friend print save as pdf

Related Stories

Physicists correct quantum errors

Feb 03, 2014

Scientists from the FOM Foundation and the Technical University Delft, working together at the Kavli Institute of Nanoscience, have succeeded in detecting and correcting errors during the storage of quantum ...

At Yale, quantum computing is a (qu)bit closer to reality

Feb 15, 2012

(PhysOrg.com) -- Physicists at Yale University have taken another significant step in the development of quantum computing, a new frontier in computing that promises exponentially faster information processing ...

Quantum computation: Fragile yet error-free

Jun 12, 2014

In a close collaborative effort, Spanish and Austrian physicists have experimentally encoded one quantum bit (qubit) in entangled states distributed over several particles and for the first time carried out ...

Three tiny qubits, another big step toward quantum computing

Sep 29, 2010

(PhysOrg.com) -- The rules that govern the world of the very small, quantum mechanics, are known for being bizarre. One of the strangest tenets is something called quantum entanglement, in which two or more objects (such ...

In quantum computing, light may lead the way

Oct 08, 2013

(Phys.org) —Light might be able to play a bigger, more versatile role in the future of quantum computing, according to new research by Yale University scientists.

Recommended for you

Quantum physics just got less complicated

Dec 19, 2014

Here's a nice surprise: quantum physics is less complicated than we thought. An international team of researchers has proved that two peculiar features of the quantum world previously considered distinct ...

Controlling light on a chip at the single-photon level

Dec 16, 2014

Integrating optics and electronics into systems such as fiber-optic data links has revolutionized how we transmit information. A second revolution awaits as researchers seek to develop chips in which individual ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

George_Rajna
Jul 14, 2014
This comment has been removed by a moderator.
ralph638s
not rated yet Jul 14, 2014
So, D-Wave sells quantum computers, yet according to this article, we haven't yet developed any reliable quantum computers, so what are those guys selling? Unreliable quantum computers?

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.