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Physical Review A

Measuring the parity of N distant atoms with linear optics

Ya-Feng Liu, Xu‐Bo Zou, Guang‐Can Guo

Published Apr 8, 2014• 0 citations
Publisher

Abstract

It is known that parity measurement, together with single-qubit rotation, is sufficient for implementing scalable quantum computation. In this Brief Report, we propose a scheme for a projective measurement of the parity operator ${P}_{z}={\ensuremath{\bigotimes}}_{i=1}^{N}{\ensuremath{\sigma}}_{i,z}$ of $N$ distant atoms trapped in spatially separated cavities. Instead of direct interaction between the atoms, quantum interference of polarized photons decaying from the optical cavities is used to realize expected measurement without resorting to a sequence of single- and two-qubit operations. It is shown that parity measurement can be implemented repeatedly until success without destroying the qubits at any stage of the operation.

DOI
10.1103/physreva.89.044301

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It is known that parity measurement, together with single-qubit rotation, is sufficient for implementing scalable quantum computation. In this Brief Report, we propose a scheme for a projective measurement of the parity operator Pz=\ensuremath⨂i=1N\ensuremathσi,z{P}_{z}={\ensuremath{\bigotimes}}_{i=1}^{N}{\ensuremath{\sigma}}_{i,z}Pz​=\ensuremath⨂i=1N​\ensuremathσi,z​ of NNN distant atoms trapped in spatially separated cavities. Instead of direct interaction between the atoms, quantum interference of polarized photons decaying from the optical cavities is used to realize expected measurement without resorting to a sequence of single- and two-qubit operations. It is shown that parity measurement can be implemented repeatedly until success without destroying the qubits at any stage of the operation.
We demonstrate the possibility to perform distributed quantum computing using only single-photon sources (atom-cavity-like systems), linear optics, and photon detectors. The qubits are encoded in stable ground states of the sources. To implement a universal two-qubit gate, two photons should be generated simultaneously and pass through a linear optics network, where a measurement is performed on them. Gate operations can be repeated until a success is heralded without destroying the qubits at any stage of the operation. In contrast with other schemes, this does not require explicit qubit-qubit interactions, a priori entangled ancillas, nor the feeding of photons into photon sources.
Abstract One of the most fascinating aspects of quantum networks is their capability to distribute entanglement as a nonlocal communication resource1. In a first step, this requires network-ready devices that can generate and store entangled states2. Another crucial step, however, is to develop measurement techniques that allow for entanglement detection. Demonstrations for different platforms3–13 suffer from being not complete, destructive or local. Here, we demonstrate a complete and nondestructive measurement scheme14–16 that always projects any initial state of two spatially separated network nodes onto a maximally entangled state. Each node consists of an atom trapped inside an optical resonator from which two photons are successively reflected. Polarization measurements on the photons discriminate between the four maximally entangled states. Remarkably, such states are not destroyed by our measurement. In the future, our technique might serve to probe the decay of entanglement and to stabilize it against dephasing via repeated measurements17,18.