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Physical Review Applied

Diamond optomechanical cavity with a color center for coherent microwave-to-optical quantum interfaces

Byunggi Kim, Hodaka Kurokawa, K. Sakai, Kazuki Koshino, Hideo Kosaka, Masahiro Nomura

Published Oct 13, 2023• 12 citations
Publisher

Abstract

Quantum transduction between microwave and optical photons plays a key role in quantum communication among remote qubits. Although the quantum transduction schemes generating communication photons have been successfully demonstrated by using optomechanical interfaces, the low conversion efficiency remains an obstacle to the implementation of a quantum network consisting of multiple qubits. Here, we present an efficient quantum transduction scheme using a one-dimensional diamond optomechanical crystal cavity tuned at a color-center emission without optomechanical coupling. The optomechanical crystal cavity incorporates a thin aluminum nitride ($\mathrm{Al}\mathrm{N}$) pad piezoelectric coupler near the concentrator cavity region, while retaining ultrasmall mechanical and optical mode volumes of about $1.5\phantom{\rule{0.1em}{0ex}}\ifmmode\times\else\texttimes\fi{}\phantom{\rule{0.1em}{0ex}}{10}^{\ensuremath{-}4}({\mathrm{\ensuremath{\Lambda}}}_{p}{)}^{3}$ and $0.2(\ensuremath{\lambda}/n{)}^{3}$, respectively. The energy level of a coherent color-center electron is manipulated by a strong mechanical-mode--color-center electron-coupling rate up to 16.4 MHz. In our system, we theoretically predict that the population-conversion efficiency from a single microwave photon into an optical photon can reach 15% combined with current technologies. The coherent conversion efficiency is over 10% with a reasonably pure decay time of ${T}_{2}^{\ensuremath{\ast}}>10\phantom{\rule{0.25em}{0ex}}\mathrm{ns}$. Our results imply that an atomic color center strongly coupled to the optomechanical crystal cavity will offer a highly efficient quantum transduction platform.

DOI
10.1103/physrevapplied.20.044037

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Quantum transduction between microwave and optical photons plays a key role in quantum communication among remote qubits. Although the quantum transduction schemes generating communication photons have been successfully demonstrated by using optomechanical interfaces, the low conversion efficiency remains an obstacle to the implementation of a quantum network consisting of multiple qubits. Here, we present an efficient quantum transduction scheme using a one-dimensional diamond optomechanical crystal cavity tuned at a color-center emission without optomechanical coupling. The optomechanical crystal cavity incorporates a thin aluminum nitride (AlN\mathrm{Al}\mathrm{N}AlN) pad piezoelectric coupler near the concentrator cavity region, while retaining ultrasmall mechanical and optical mode volumes of about 1.5\ifmmode×\else\texttimes\fi10\ensuremath−4(\ensuremathΛp)31.5\phantom{\rule{0.1em}{0ex}}\ifmmode\times\else\texttimes\fi{}\phantom{\rule{0.1em}{0ex}}{10}^{\ensuremath{-}4}({\mathrm{\ensuremath{\Lambda}}}_{p}{)}^{3}1.5\ifmmode×\else\texttimes\fi10\ensuremath−4(\ensuremathΛp​)3 and 0.2(\ensuremathλ/n)30.2(\ensuremath{\lambda}/n{)}^{3}0.2(\ensuremathλ/n)3, respectively. The energy level of a coherent color-center electron is manipulated by a strong mechanical-mode--color-center electron-coupling rate up to 16.4 MHz. In our system, we theoretically predict that the population-conversion efficiency from a single microwave photon into an optical photon can reach 15% combined with current technologies. The coherent conversion efficiency is over 10% with a reasonably pure decay time of T2\ensuremath∗>10ns{T}_{2}^{\ensuremath{\ast}}>10\phantom{\rule{0.25em}{0ex}}\mathrm{ns}T2\ensuremath∗​>10ns. Our results imply that an atomic color center strongly coupled to the optomechanical crystal cavity will offer a highly efficient quantum transduction platform.
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Scaling up superconducting quantum processors remains a central challenge for realizing fault-tolerant quantum computation. Although distributed architectures based on optical photons offer a promising route to scalability, they require an efficient microwave-to-optical quantum transducer that operates at cryogenic temperatures. Existing approaches typically rely on strong optical pumping, which induces undesirable heating and degrades single-photon coherence. Here, we propose a microwave-to-optical quantum transducer based on resonant scattering at a single color center embedded in a diamond optomechanical resonator. We show that strong coupling between the color center and the optical cavity enables coherent conversion at extremely weak pump powers on the order of 10 pW. The proposed scheme enables remote entanglement generation at a kilohertz-scale rate with a fidelity exceeding 0.9, demonstrating a viable pathway toward ultra-weak-pump and high-efficiency quantum transducers based on a solid-state defect.
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Piezoelectric optomechanical platforms represent one of the most promising routes toward achieving quantum transduction of photons between the microwave and optical frequency domains. However, there are significant challenges to achieving near-unity transduction efficiency. The authors discuss such factors in the context of the two main approaches being pursued for high efficiency transduction. The first approach uses 1D nanobeam optomechanical crystals excited by interdigitated transducers and is characterized by large single-photon optomechanical coupling strength, limited intracavity pump photon population to avoid absorption-induced heating (at cryogenic temperature), and low phonon injection efficiency from the transducer to the optomechanical cavity. The second approach uses (quasi) bulk acoustic wave resonators integrated into photonic Fabry–Perot cavity geometries and is characterized by low single-photon optomechanical coupling strength, high intracavity pump photon population without significant heating, and high phonon injection efficiency. After reviewing the current status of both approaches, the need for co-designing the electromechanical and optomechanical sub-systems is discussed in order to achieve high transduction efficiencies, taking the GaAs piezo-optomechanical platform as an example.
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