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arXiv:1710.06269 · Physical Review A

Heralded entangling quantum gate via cavity-assisted photon scattering

Halyne Silva Borges, Daniel Z. Rossatto, F. S. Luiz, Celso J. Villas-Bôas

Published Jan 18, 2018• 10 citations
arXivHTMLPDF

Abstract

We theoretically investigate the generation of heralded entanglement between two identical atoms via cavity-assisted photon scattering in two different configurations, namely, either both atoms confined in the same cavity or trapped into locally separated ones. Our protocols are given by a very simple and elegant single-step process, the key mechanism of which is a controlled-phase-flip gate implemented by impinging a single photon on single-sided cavities. In particular, when the atoms are localized in remote cavities, we introduce a single-step parallel quantum circuit instead of the serial process extensively adopted in the literature. We also show that such parallel circuit can be straightforwardly applied to entangle two macroscopic clouds of atoms. Both protocols proposed here predict a high entanglement degree with a success probability close to unity for state-of-the-art parameters. Among other applications, our proposal and its extension to multiple atom-cavity systems step toward a suitable route for quantum networking, in particular for quantum state transfer, quantum teleportation, and nonlocal quantum memory.

DOI
10.1103/physreva.97.013828

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We propose a scheme to achieve a parallelized controlled-NOT (c-not) gate based on electromagnetically induced transparency (EIT) and cavity-assisted photon scattering. By using the flying photon as the control bit, we can implement a conditional transfer between two logical states of an atom trapped in the cavity with high fidelity and on a microsecond time scale. Thanks to the fact that the photon is well suited for scalable quantum computation, a quantum c-not gate between the single-photon pulses and the nonlocal gate on remote atoms are obtained by reflecting the photon pulse from an optical cavity with a single-trapped atom. Our protocol is robust for spontaneous emission and works quite well in the bad-cavity limit, which makes it more applicable in the laboratory with current experimental techniques.
We theoretically investigate the implementation of a quantum controlled-phase gate in a system constituted by a single atom inside an optical cavity, based on the electromagnetically induced transparency effect. First we show that a probe pulse can experience a $\ensuremath{\pi}$ phase shift due to the presence or absence of a classical control field. Considering the interplay of the cavity-EIT effect and the quantum memory process, we demonstrated a controlled-phase gate between two single photons. To this end, first one needs to store a (control) photon in the ground atomic states. In the following, a second (target) photon must impinge on the atom-cavity system. Depending on the atomic state, this second photon will be either transmitted or reflected, acquiring different phase shifts. This protocol can then be easily extended to multiphoton systems, i.e., keeping the control photon stored, it may induce phase shifts in several single photons, thus enabling the generation of multipartite entangled states. We explore the relevant parameter space in the atom-cavity system that allows the implementation of quantum controlled-phase gates using the recent technologies. In particular, we have found a lower bound for the cooperativity of the atom-cavity system which enables the implementation of phase shift on single photons. The induced shift on the phase of a photonic qubit and the controlled-phase gate between single photons, combined with optical devices, enable one to perform universal quantum computation.
Quantum gates are the building blocks of quantum circuits, which in turn are the cornerstones of quantum information processing. In this work, we theoretically investigate a single-step implementation of both a universal two- (cnot) and three-qubit (quantum Fredkin) gates in a cross-cavity setup coupled to a $\mathrm{\ensuremath{\Lambda}}$-type three-level atom. Within a high-cooperativity regime, the system exhibits an atomic-state-dependent $\ensuremath{\pi}$-phase gate involving the two-mode single-photon bright and dark states of the input light pulses. This allows for the controlled manipulation of light states by the atom and vice versa. Our results indicate these quantum gates can be implemented with high probability of success using the state-of-the-art parameters, either for the weak- or strong-coupling regime, where the quantum interference is due to an electromagnetically induced transparencylike phenomenon and the Autler-Townes splitting, respectively. This work not only paves the way for implementing quantum gates in a single step using simple resources, thus avoiding the need to chain basic gates together in a circuit, but it also endorses the potential of cross-cavity systems for realizing universal quantum computation.
We study the entanglement dynamics between two spatially separated atoms trapped in two separate optical cavities. Based on cavity-assisted interactions between the atoms and separated photonic pulses, we propose a scheme for the implemention of a controlled-phase-flip gate (CPF gate) between each of the atoms and the photonic pulse to protect the remote atomic quantum entanglement against the decaying caused by spontaneous emission. What we need to do is to shoot the horizontally polarized photons onto the cavity mirror successively, plus a train of Hadamard operations on the atoms, and no measurement is needed here. It is shown that the quantum entanglement of the two remote atoms can be protected effectively in this way. We also extend our scheme to the case of weak coupling and low Q cavity cases. The simplicity of the current scheme may warrant its experimental realization.
Quantum networks involving multiqubit entanglement allow exciting applications in quantum communication, quantum sensing, and distributed quantum computation. The efficiency of nonlocal entanglement generation through optical channels drops exponentially with the distance between network nodes. We present a parallel and heralded protocol for generating distributed multiqubit entanglement across multiple nodes. This is achieved by using a high-dimensional single photon that works as a common-data bus connecting all stationary qubits (i.e., silicon-vacancy electron spins), each of which is coupled to a single-sided optical cavity. Parallel multiqubit entangled states are heralded by the detection of the single photon after it interacts with each stationary qubit and passes through each photonic modulation circuit. This parallel protocol can significantly improve the efficiency of distributed entanglement generation and provides a viable route towards distributed multinode quantum networks.