[論文レビュー] Coherent control of a superconducting qubit using light

Hana K. Warner, Jeffrey Holzgrafe+16 more|arXiv (Cornell University)|Oct 24, 2023

Quantum Information and Cryptography被引用数 9

ひとこと要約

tldr: 本論文は、薄膜リチウムニオブ酸化物腔電気光トランスデューサを用いた超導量子ビットのコヒーレント光制御を実証し、変換効率1.18%および2.27 MHzの光駆動の量子ビットラビ振動を達成しつつ、量子ビットのコヒーレンスを劣化させないことを示している。

ABSTRACT

Quantum communications technologies require a network of quantum processors connected with low loss and low noise communication channels capable of distributing entangled states. Superconducting microwave qubits operating in cryogenic environments have emerged as promising candidates for quantum processor nodes. However, scaling these systems is challenging because they require bulky microwave components with high thermal loads that can quickly overwhelm the cooling power of a dilution refrigerator. Telecommunication frequency optical signals, meanwhile, can be fabricated in significantly smaller form factors while avoiding challenges due to high signal loss, noise sensitivity, and thermal loads due to their high carrier frequency and propagation in silica optical fibers. Transduction of information via coherent links between optical and microwave frequencies is therefore critical to leverage the advantages of optics for superconducting microwave qubits, while also enabling superconducting processors to be linked with low-loss optical interconnects. Here, we demonstrate coherent optical control of a superconducting qubit. We achieve this by developing a microwave-optical quantum transducer that operates with up to 1.18% conversion efficiency with low added microwave noise, and demonstrate optically-driven Rabi oscillations in a superconducting qubit.

研究の動機と目的

• Motivate interfacing superconducting qubits with optical photons to enable long-distance quantum networking and reduced cryogenic heat load.
• Develop and characterize a cavity electro-optic transducer in thin-film lithium niobate that coherently mediates microwave-optical energy exchange.
• Demonstrate optically driven qubit control with preserved qubit coherence times and readout fidelity.
• Assess the transducer-qubit interface performance and discuss pathways toward networked quantum processor nodes.

提案手法

• Implement a triply-resonant microwave-optical transducer using a Nb microwave LC resonator coupled to two hybridized lithium niobate optical racetrack resonators.
• Use a strong optical pump at the red mode and an optical idler at the blue mode to drive difference-frequency generation that yields a microwave tone at the qubit frequency.
• Dispersively couple the superconducting qubit to a readout resonator and perform room-temperature readout of the qubit state.
• Measure on-chip conversion efficiency and cooperativity from the microwave-to-optical and optical-to-microwave conversions.
• Perform pulsed optical driving to generate microwave pulses that drive the qubit and characterize power and time-domain Rabi oscillations.
• Analyze the impact of transducer operation on qubit coherence times and readout fidelity.

Fig. 1: Transducer-driven superconducting qubit scheme. (a) Two optical fields ( $\omega_{\pm}$ ) are coupled into the transducer via a waveguide. The two modes are resonant with the transducer’s hybridized optical modes which are generated by a coupled paperclip resonator capacitively coupled ( $C_

実験結果

リサーチクエスチョン

• RQ1 Can a thin-film electro-optic transducer coherently convert between microwave and optical domains with sufficient performance to drive a superconducting qubit?
• RQ2 What are the conversion efficiency, cooperativity, and bandwidth achievable in a triply-resonant CEO-MOQT integrated with a superconducting qubit?
• RQ3 Does optically driven qubit control preserve qubit coherence times and readout performance compared to conventional RF control?
• RQ4 What are the prospects and requirements for using such transducers to network superconducting quantum processor nodes via optical channels.

主な発見

• Achieved on-chip microwave-to-optical and optical-to-microwave conversion efficiency of about 1.18% at -13.8 dBm optical pump power (44.2 μW on-chip).
• Measured microwave-optical coupling rate g_eo/2π ≈ 945 Hz with cooperativity up to 1.16%.
• Demonstrated optically driven Rabi oscillations in a superconducting qubit with a Rabi frequency of 2.27 MHz and a π-pulse duration around 220 ns.
• Qubit coherence times (T1 ≈ 8 μs, T2* ≈ 800 ns) are not degraded by transducer operation under the tested regime.
• Found that transducer-driven control yields a qubit linewidth around 645 kHz and a qubit frequency near 3.703 GHz in CW spectroscopy, with clear chevron-type Rabi behavior in time-domain measurements.

Fig. 2: CEO-MOQT. (a) Optical micrograph of transducer. A niobium (Nb) microwave LC resonator (silver) is capacitively coupled to two hybridized lithium niobate racetrack resonators in a paperclip geometry (black) to coherently exchange energy between the microwave and optical domains using the reso