Synopsis: Hitting Reset After a Quantum Measurement

Quantum information lost after a measurement can be recovered using quantum error correction methods.
Synopsis figure
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


Features

More Features »

Announcements

More Announcements »

Subject Areas

Quantum Information

Previous Synopsis

Next Synopsis

Particles and Fields

Higgs-like Particle in a Mirror

Read More »

Related Articles

Synopsis: Traveling with a Quantum Salesman
Quantum Information

Synopsis: Traveling with a Quantum Salesman

Quantum computing could speed up certain algorithms for solving the famous traveling salesman problem. Read More »

Synopsis: Prepping an Entanglement Witness
Quantum Information

Synopsis: Prepping an Entanglement Witness

Researchers have devised an improved method for checking whether two particles are entangled.     Read More »

Synopsis: Strong Light-Matter Coupling in a Hybrid System
Quantum Information

Synopsis: Strong Light-Matter Coupling in a Hybrid System

A system combining a quantum dot and a superconducting cavity achieves the strongest light-matter coupling for this type of hybrid system.   Read More »

More Articles