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arXiv:1902.08344 · Physical Review A

Quantum entanglement distribution with hybrid parity gate

Feng Mei, Ya‐Fei Yu, Xun‐Li Feng, Zhi‐Ming Zhang, C. H. Oh

Published Nov 16, 2010• 34 citations
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Abstract

We propose a scheme for entanglement distribution among different single atoms trapped in separated cavities. In our scheme, by reflecting an input coherent optical pulse from a cavity with a single trapped atom, a controlled phase-shift gate between the atom and the coherent optical pulse is achieved. Based on this gate and homodyne detection, we construct an $n$-qubit parity gate and show its use for the distribution of a large class of entangled states in one shot, including the GHZ state $|{\mathrm{GHZ}}_{n}\ensuremath{\rangle}$, $W$ state $|{W}_{n}\ensuremath{\rangle}$, Dicke state $|{D}_{n,k}\ensuremath{\rangle}$, and certain sums of Dicke states $|{G}_{n,k}\ensuremath{\rangle}$. We also show that such a distribution could be performed with high success probability and high fidelity even in the presence of channel loss.

DOI
10.1103/physreva.82.052315

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We propose a scheme for entanglement distribution among different single atoms trapped in separated cavities. In our scheme, by reflecting an input coherent optical pulse from a cavity with a single trapped atom, a controlled phase-shift gate between the atom and the coherent optical pulse is achieved. Based on this gate and homodyne detection, we construct an nnn-qubit parity gate and show its use for the distribution of a large class of entangled states in one shot, including the GHZ state ∣GHZn\ensuremath⟩|{\mathrm{GHZ}}_{n}\ensuremath{\rangle}∣GHZn​\ensuremath⟩, WWW state ∣Wn\ensuremath⟩|{W}_{n}\ensuremath{\rangle}∣Wn​\ensuremath⟩, Dicke state ∣Dn,k\ensuremath⟩|{D}_{n,k}\ensuremath{\rangle}∣Dn,k​\ensuremath⟩, and certain sums of Dicke states ∣Gn,k\ensuremath⟩|{G}_{n,k}\ensuremath{\rangle}∣Gn,k​\ensuremath⟩. We also show that such a distribution could be performed with high success probability and high fidelity even in the presence of channel loss.
Based on the interference effect of polarized photons leaking out of separate cavities, we propose schemes for the generation of the N -atom Greenberger–Horne–Zeilinger (GHZ) state, three-atom W state and a genuine four-atom entangled state |χ⟩. In these schemes, each of the atoms is trapped separately in a remote optical cavity, and the possible spontaneous channels induced by the excited atoms lead to the coherent superposition of the states of the atoms. The desired multipartite entangled states can be generated with a certain success probability by the subsequent detection of the polarized photons in different modes. The schemes would be useful steps towards long-distance quantum communication, distributed quantum computation and constructing remote quantum information processing networks.
We describe a system for long-distance distribution of quantum entanglement, in which coherent light with large average photon number interacts dispersively with single, far-detuned atoms or semiconductor impurities in optical cavities. Entanglement is heralded by homodyne detection using a second bright light pulse for phase reference. The use of bright pulses leads to a high success probability for the generation of entanglement, at the cost of a lower initial fidelity. This fidelity may be boosted by entanglement purification techniques, implemented with the same physical resources. The need for more purification steps is well compensated for by the increased probability of success when compared to heralded entanglement schemes using single photons or weak coherent pulses with realistic detectors. The principal cause of the lower initial fidelity is fibre loss; however, spontaneous decay and cavity losses during the dispersive atom–cavity interactions can also impair performance. We show that these effects may be minimized for emitter-cavity systems in the weak-coupling regime as long as the resonant Purcell factor is larger than one, the cavity is over-coupled, and the optical pulses are sufficiently long. We support this claim with numerical, semiclassical calculations using parameters for three realistic systems: optically bright donor-bound impurities such as 19 F:ZnSe with a moderate- Q microcavity, the optically dim 31 P:Si system with a high- Q microcavity, and trapped ions in large but very high- Q cavities.
Individual atoms in optical cavities can provide an efficient interface between stationary qubits and flying qubits (photons), which is an essential building block for quantum communication. Furthermore, cavity-assisted controlled-not (cnot) gates can be used for swapping entanglement to long distances in a quantum repeater setup. Nonetheless, dissipation introduced by the cavity during the cnot may increase the experimental difficulty in obtaining long-distance entanglement distribution using these systems. We analyze and compare a number of cavity-based repeater schemes combining various entanglement generation schemes and cavity-assisted cnot gates. We find that a scheme, where high-fidelity entanglement is first generated in a two-photon detection scheme and then swapped to long distances using a recently proposed heralded controlled-ZZZ (cz) gate, exhibits superior performance compared to the other schemes. The heralded gate moves the effect of dissipation from the fidelity to the success probability of the gate thereby enabling high-fidelity entanglement swapping. As a result, high-rate entanglement distribution can be achieved over long distances even for low cooperativities of the atom-cavity systems. This high-fidelity repeater is shown to outperform the other cavity-based schemes by up to two orders of magnitude in the rate for realistic parameters and large distances (1000 km).
We propose a scheme for long-distance quantum state transfer between different atoms based on cavity-assisted interactions. In our scheme, a coherent optical pulse sequentially interacts with two distant atoms trapped in separated cavities. Through the measurement of the state of the first atom and the homodyne detection of the final output coherent light, the quantum state can be transferred into the second atom with a success probability of unity and a fidelity of unity. In addition, our scheme neither requires the high- Q cavity working in the strong coupling regime nor employs the single-photon quantum channel, which greatly relaxes the experimental requirements.
The scheme was proposed to generate multiple-atom GHZ state via the state-of-the-art two-sided cavities.A single-photon pulse could not only be reflected but also be transmitted through the two-sided cavity with a single trapped atom,which is in certain state.Entanglement between the trapped atom and the input field was resulted in this property.The numerical simulations showed that the produced multiple-particle GHZ state had high fidelity and success probability.The intrinsic noise,such as the atomic spontaneous emission,only led to the error probability and had no influence on the fidelity.In addition,the high-Q cavity and the Lamb-Dicke condition of atom were not required,which expanded the possibility of experimental realization.
We present an atomic-state entangler with single atoms trapped in separated low-Q cavities, a coherent optical pulse as a quantum channel, a photon detector that only distinguishes the vacuum and nonvacuum states, and basic optical elements based on the input–output process in the intermediate coupling region with a higher probability and fidelity. The atomic-state entangler is meaningful because it does not need a strong coupling cavity and a single-photon source and could be feasible for large-scale quantum computation and quantum communication in the future. Based on this entangler, quantum information nonlocal transfer without classical communication, the quantum controlled-NOT gate, the four-particle |χ〉 state, the N-particle Greenberger-Horne-Zeilinger (GHZ) state, and cluster-state generation can be realized completely, which is useful in large-scale and nonlocal quantum information processing.