Synopsis

Hitting Reset After a Quantum Measurement

Physics 6, s26
Quantum information lost after a measurement can be recovered using quantum error correction methods.
P. Schindler et al., Phys. Rev. Lett. (2013)

Measuring a quantum object singles out a quantum state from a set of possible states. The process is irreversible, since the object retains no information about its premeasurement uncertainty. However, a group of physicists have devised a kind of “data recovery” process based on error correction techniques used in quantum computing. As described in Physical Review Letters, they measured one part of an entangled quantum system and then used the other, unmeasured part to reset everything to the preobserved state.

In a quantum computer, the unit of information is a qubit that exists in two states, “zero” and “one,” at the same time. This superposition is not directly observable, since measuring a qubit can only return either “zero” or “one.” The initial state is irretrievable once a measurement is made, making it impossible to backup (or “clone”) a qubit to compensate for errors in quantum computing. However, by entangling multiple qubits, quantum error correction creates a cross-check for spotting data corruption.

Errors and measurements induce similar changes to a quantum system. Therefore, Philipp Schindler of the University of Innsbruck in Austria and his colleagues adapted an error correction protocol to recover quantum information following a measurement. They started by encoding an arbitrary initial state on a system of three trapped calcium ions. They then temporarily excited two of the ions to energetically isolate them from a light beam that measured whether the third ion was in the “zero” or “one” state. To undo the effects of this measurement, the team re-cooled the ion and then re-imprinted the initial state using the two unmeasured ions. The final three-ion configuration matched the original at a level of around 84%. – Michael Schirber


Subject Areas

Quantum Information

Related Articles

Pushing the Limits of Quantum Sensing with Variational Quantum Circuits
Quantum Information

Pushing the Limits of Quantum Sensing with Variational Quantum Circuits

Variational quantum algorithms could help researchers improve the performance of optical atomic clocks and of other quantum-metrology schemes. Read More »

Using Quantum Dots to Simulate Magnetism
Quantum Physics

Using Quantum Dots to Simulate Magnetism

Researchers successfully use an array of quantum dots to create and study a Heisenberg spin chain. Read More »

Quantum Leap for Quantum Primacy
Quantum Physics

Quantum Leap for Quantum Primacy

Two experimental quantum computers tackle the most complex problems yet, suggesting an end to the debate on whether quantum “primacy”—the point at which a quantum computer outperforms the best possible classical computer—can be reached. Read More »

More Articles