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Pulsed atom-mechanical quantum non-demolition gate

A. D. Manukhova, Andrey A. Rakhubovsky, Radim Filip

Published Jan 8, 2020• 4 citations
Publisher

Abstract

Abstract Hybridization of quantum science and technology crucially depends on quantum gates between various physical systems. The different platforms have different fundamental physics and, therefore, diverse advantages in various applications. Many applications require nearly ideal quantum gates with variable large interaction gain and sufficient entangling power. Moreover, pulsed gates are advantageous for fast quantum circuits. For quantum systems with continuous variables, the quantum non-demolition (QND) gate is the most basic. It is an entangling gate that simultaneously keeps a variable of the interacting system unchanged. This feature is useful for quantum circuits from quantum sensing to continuous variable quantum computing. Currently, atomic ensembles storing quantum states of radiation and mechanical oscillators transducing them are two major but very different continuous-variable matter platforms. We propose a high-quality continuous-variable QND gate between an atomic ensemble and a mechanical oscillator in the separated optical cavities connected by propagating optical pulses. We demonstrate that squeezing of light pulses, homodyne measurement, and optimized feedforward control used to build the gate are sufficient to reach an interaction gain up to 50 with nearly ideal entangling power.

DOI
10.1038/s41534-019-0229-9

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Abstract Hybridization of quantum science and technology crucially depends on quantum gates between various physical systems. The different platforms have different fundamental physics and, therefore, diverse advantages in various applications. Many applications require nearly ideal quantum gates with variable large interaction gain and sufficient entangling power. Moreover, pulsed gates are advantageous for fast quantum circuits. For quantum systems with continuous variables, the quantum non-demolition (QND) gate is the most basic. It is an entangling gate that simultaneously keeps a variable of the interacting system unchanged. This feature is useful for quantum circuits from quantum sensing to continuous variable quantum computing. Currently, atomic ensembles storing quantum states of radiation and mechanical oscillators transducing them are two major but very different continuous-variable matter platforms. We propose a high-quality continuous-variable QND gate between an atomic ensemble and a mechanical oscillator in the separated optical cavities connected by propagating optical pulses. We demonstrate that squeezing of light pulses, homodyne measurement, and optimized feedforward control used to build the gate are sufficient to reach an interaction gain up to 50 with nearly ideal entangling power.
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Feasible setup for pulsed quantum nondemolition interaction between two distant mechanical oscillators through an optical or microwave mediator is proposed. The proposal uses homodyne measurement of the mediator and feedforward control of the mechanical oscillators to reach the interaction. To verify the quantum nature of the interaction, we investigate the Gaussian entanglement generated in the mechanical modes. We evaluate it under influence of mechanical bath and propagation loss for the mediator and propose ways to optimize the interaction. Finally, both currently available optomechanical and electromechanical platforms are numerically analyzed. The analysis shows that implementation is already feasible with current technology.
Hybrid systems hold promise to provide an advantage in future quantum technology. Operating such systems outside the classical regime is crucially important to fully realize their potential. We investigate a pulsed quantum nondemolition gate between a cloud of atoms and a mechanical oscillator in distant cavities and demonstrate that this gate is capable of producing nonclassical coincidences of excitations in the disparate subsystems interacting by light. The nonclassicality is justified by evaluation of excitations created simultaneously in both modes beyond any joint classical states of such subsystems. To test the result, we use a nonclassicality witness based on available homodyne tomography of the atomic and mechanical states. Using feasible parameters, we show that it is possible to turn the pulsed dynamics of the state-of-the-art systems into nonclassical coincidences, and illustrate it for the cases of the atom-light, optomechanical, and atom-mechanical hybrid interactions. These tests are necessary to open full investigation of quantum correlations in hybrid systems. Published by the American Physical Society 2024
The sum gate is the canonical two-mode gate for universal quantum computation based on continuous quantum variables. It represents the natural analogue to a qubit C-NOT gate. In addition, the continuous-variable gate describes a quantum nondemolition (QND) interaction between the quadrature components of two light modes. We experimentally demonstrate a QND sum gate, employing the scheme by R. Filip, P. Marek, and U. L. Andersen [Phys. Rev. A 71, 042308 (2005)10.1103/PhysRevA.71.042308], solely based on off-line squeezed states, homodyne measurements, and feedforward. The results are verified by simultaneously satisfying the criteria for QND measurements in both conjugate quadratures.
The continuous-variable controlled-ZZZ gate is a canonical two-mode gate for universal continuous-variable quantum computation. It is considered as one of the most fundamental continuous-variable quantum gates. Here we present a scheme for realizing continuous-variable controlled-ZZZ gate between two optical beams using an atomic ensemble. The gate is performed by simply sending the two beams propagating in two orthogonal directions twice through a spin-squeezed atomic medium. Its fidelity can run up to one if the input atomic state is infinitely squeezed. Considering the noise effects due to atomic decoherence and light losses, we show that the observed fidelities of the scheme are still quite high within presently available techniques.
Quantum coupling between mechanical oscillators and atomic gases generating entanglement has been recently experimentally demonstrated using their subsequent interaction with light. The next step is to build a hybrid atom-mechanical quantum gate showing bosonic interference effects of single quanta in the atoms and oscillators. We propose an experimental test of Hong-Ou-Mandel interference between single phononic excitation and single collective excitation of atoms using the optical connection between them. A single optical pulse is sufficient to build a hybrid quantum-nondemolition gate to observe the bunching of such different quanta. The output atomic-mechanical state exhibits a probability of a hybrid bunching effect that proves its nonclassical aspects. This proposal opens a feasible road to broadly test such advanced quantum bunching phenomena in a hybrid system with different specific couplings.