A nondestructive Bell-state measurement on two distant atomic qubits

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.

Deterministic Bell state measurement with a single quantum memory

“…The development of large-scale distributed quantum computers requires quantum networks [1][2][3] based on remote entanglement to connect the computers [4][5][6][7][8][9][10] and thus requires quantum repeaters [11][12][13][14] or quantum interfaces 15 that can perform a deterministic and complete Bell state measurement (BSM) [16][17][18][19] not only to extend the distance of photon transmission and to route photons over the networks but also to interface the quantum state between photons and qubits in quantum computers 15,[20][21][22] . A complete BSM allows us to project any two-qubit states into one of the four Bell states deterministically, which typically requires quantum nondemolition measurement known as single-shot measurement [23][24][25][26][27][28] .…”

Chiral Quantum Optics and Optical Nonreciprocity Based on Susceptibility‐Momentum Locking

“…[4][5][6] Nonreciprocal optical devices, such as isolators and circulators, can block or divert the backward signal light and thus promise many important applications in classical optical systems. [7][8][9][10] They are often the crucial function elements in quantum computation, [11][12][13][14] quantum measurement, [15][16][17][18] and quantum networks. [19][20][21][22] A typical matured optical isolator is the Faraday rotator based on the magneto-optical effect.…”

Bell-state measurement exceeding 50% success probability with linear optics

“…In atomic systems, complete BSMs have been performed [5,6,31,32]. However, these require intricate experimental set-ups that are challenging to scale up.…”

“…For the single-photon-based qubit approach, both scalability and fault tolerance in quantum communication and computing heavily depend on the BSM efficiencies. In this case, the 50% limit has been overcome in proof-of-principle experiments by exploiting hyperentanglement [34][35][36] and incorporating nonlinear elements [4,5,32,37]. A third approach that has been suggested in theory is based on adding additional ancillary photons to a linear-optics setup [38,39] and using photon-number resolving detectors, offering clear advantages regarding lower experimental complexity and higher scalability.…”