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Physical Review A

Engineering two-mode continuous-variable entangled states of distant atomic spin ensembles with superconducting quantum circuits

Fuli Li, Shaoyan Gao, Fuli Li

Published Jan 30, 2012• 10 citations
Publisher

Abstract

We present an experimental feasible scheme to generate two-mode entangled states of two spatially separated atomic spin ensembles, using superconducting quantum circuits consisting of two coplanar waveguide resonators and a charge qubit. We show that, with the charge qubit as a tunable coupler and the resonator modes as a quantum bus, the collective atomic spins can be steered into a two-mode squeezed state exhibiting Einstein-Podolsky-Rosen entanglement through adiabatic following of the ground state of the system.

DOI
10.1103/physreva.85.014303

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We present an experimental feasible scheme to generate two-mode entangled states of two spatially separated atomic spin ensembles, using superconducting quantum circuits consisting of two coplanar waveguide resonators and a charge qubit. We show that, with the charge qubit as a tunable coupler and the resonator modes as a quantum bus, the collective atomic spins can be steered into a two-mode squeezed state exhibiting Einstein-Podolsky-Rosen entanglement through adiabatic following of the ground state of the system.
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We study controllable generation of two-mode-entangled states in a circuit QED setup, which consists of two spatially separated superconducting transmission line resonators and a single gap-tunable superconducting qubit. Two sharp coupling sidebands are induced when the artificial atom is suitably driven by a bichromatic microwave field. The two resonators can have squeezing-type interactions with the qubit via the coupling sidebands. If the two resonators are not degenerate, we show that the two resonators can be cooled down into the two-mode squeezed vacuum via dissipation of the qubit. The generation of the two-mode squeezed state is based on a dissipative state-engineering process, which explores the energy relaxation of the qubit as a resource. Moreover, the scheme does not need both the specific preparation of the initial state and the designed special dynamical process of the system. If the resonators are degenerate, we show that entangled coherent states of the resonators can be generated by use of the unitary dynamical evolution process of the system and the state-projection measurement. Moreover, macro entangled coherent states of the resonators with huge photons can in principle be created if the resonators and the qubit have sufficiently long lifetimes. The present scheme has two remarkable features: (1) only a single qubit is used in the generation of the two-mode squeezed state; and (2) the ultrastrong coupling condition and initializing the resonators in coherent states are not required. These make the present scheme more simple and feasible in experimental implementation.
We present a scheme to engineer a two-mode squeezed state of effective bosonic modes realized by collective excitations of two distant nitrogen-vacancy-center ensembles (NVEs) coupled to separated transmission line resonators (TLRs), which are interconnected by a current-biased Josephson-junction superconducting qubit. By making use of the engineered NVE-TLR magnetic coupling with Raman transition between the ground sublevels of the NVEs, we may manipulate the artificial reservoir by tuning the external driving fields. The TLR decay induces an artificial reservoir, which can drive the system to the desired entangled squeezed states. Our idea provides a scalable way to a NVE-based continuous-variable quantum-information processing, which is close to being achievable with currently available technology.
We propose an efficient method for generating two-mode squeezed states of the collective excitation of two nitrogen-vacancy-center ensembles (NVEs), which are magnetically coupled to two interacting superconducting transmission line resonators via photon hopping, respectively. By applying the external driving fields to induce Raman transitions between the ground-state sublevels of the nitrogen-vacancy center, an effective interaction between the spin ensembles and the resonators can be engineered. We show that the dissipative quantum dynamical process of the two resonators can be employed to steer the two NVEs into a two-mode squeezed state. By comparison with previous proposals, our scheme does not need either an extra superconducting qubit, or external squeezing resource. The present work may have potential applications for implementing NVE-based hybrid quantum computation.
We propose an efficient scheme for the generation of two-mode squeezed states for two separated atomic ensembles trapped in distant cavities. The scheme is based on selective couplings between the collective atomic modes and two linearly transformed common field modes mediated by an optical fiber or a third cavity. The quanta of the transformed atomic modes are exhausted due to the linear coupling with the transformed field modes, bringing the original atomic modes into the two-mode squeezed states. The experimental implementation of the scheme would be an important step toward quantum communication and networking with continuous variables.
We present a protocol for deterministically generating an optimal two-mode-squeezed state of distant free-space atomic ensembles. The protocol relies on two passes of a single coherent pulse through two separate atomic ensembles placed in homogeneous magnetic fields. In contrast to previous single-pass schemes, our approach significantly enhances the degree of entanglement due to the exponential behavior of the Einstein-Podolsky-Rosen variance. We also provide an efficient scheme to perform Bell measurement of atomic states, enabling the implementation of high-fidelity atomic quantum teleportation.