Experimental entanglement of six photons in graph states

Abstract

Graph states are special kinds of multipartite entangled states that correspond to mathematical graphs where the vertices take the role of quantum spin systems and the edges represent interactions. They not only provide an efficient model to study multiparticle entanglement, but also find wide applications in quantum error correction, multi-party quantum communication and most prominently, serve as the central resource in one-way quantum computation. Here we report the creation of two special instances of graph states, the six-photon Greenberger-Horne-Zeilinger states -- the largest photonic Schr\"{o}dinger cat, and the six-photon cluster states-- a state-of-the-art one-way quantum computer. Flexibly, slight modifications of our method allow creation of many other graph states. Thus we have demonstrated the ability of entangling six photons and engineering multiqubit graph states, and created a test-bed for investigations of one-way quantum computation and studies of multiparticle entanglement as well as foundational issues such as nonlocality and decoherence

Disorder overtakes order in information concentration over quantum networks

“…The results displayed until now are all for systems of eight spins, and this is dictated by the approximate number of spins which can be experimentally accessed coherently in quantum systems. However, such boundaries are steadily being extended and improved [7,8,11,12,[45][46][47][48]. In this light, it is important to mention here that the results obtained in this paper are resilient with respect to moderate changes of the total number of spins.…”

“…Moreover, photonic systems are widely envisaged as the substrates for quantum communication protocols, and in that case, currently available technology limitations are even stricter on the number of qubits [47,48]. We have therefore focused our attention on quantum communication protocols involving 7 or 8 parties , constituting the sending and receiving ports of the communication protocol.…”

Optimal collinear Gaussian beams for spontaneous parametric down-conversion

“…A number of applications of SPDC photons, including the generation of multiphoton entangled states for quantum computing [23][24][25][26], involve interference between photons from separate (and nominally identical) SPDC sources. The success of such applications depends not only on the efficiency of SPDC photon production, but also on the degree of mutual coherence of photons from independent sources [27,28].…”

Experimental generation of an eight-photon Greenberger–Horne–Zeilinger state

“…In particular, polarization-entangled Einstein-Podolsky-Rosen (EPR) pairs are often used as the basic blocks for generating multi-photon entangled states or as resources for performing quantum teleportation tasks. A number of experiments involving two photon pairs [1][2][3][4][5][6][7][8] and a few experiments involving five photons (two photon pairs plus one single photon) 9 or three photon pairs [10][11][12][13] have been carried out to demonstrate various protocols in quantum communication and linear optical quantum computing. Typical systems for two-photon-pair experiments use a frequency-doubled Ti:sapphire mode-locked laser as a pump, with a repetition rate of ~80 MHz, a pulse duration of ~150 fs, and an operating wavelength of ~400 nm.…”