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


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: Making Hard Problems for Quantum Computers
Quantum Information

Synopsis: Making Hard Problems for Quantum Computers

Researchers have developed a computer algorithm that doesn’t solve problems but instead creates them for the purpose of evaluating quantum computers. Read More »

Viewpoint: A Bird’s Eye View of Circuit Photons
Quantum Information

Viewpoint: A Bird’s Eye View of Circuit Photons

A scanning probe detects the quantum states of photons in a microwave circuit, providing the information needed for quantum simulations. Read More »

Viewpoint: Hiding a Quantum Cache in Diamonds
Quantum Information

Viewpoint: Hiding a Quantum Cache in Diamonds

Entanglement purification, a vital enabler for practical quantum networks, has been shown to be feasible with secluded nuclear memories in diamond. Read More »

More Articles