Abstract
Conversion of electrical and optical signals lies at the foundation of the global internet. Such converters are used to extend the reach of long-haul fibre-optic communication systems and within data centres for high-speed optical networking of computers. Likewise, coherent microwave-to-optical conversion of single photons would enable the exchange of quantum states between remotely connected superconducting quantum processors1. Despite the prospects of quantum networking2, maintaining the fragile quantum state in such a conversion process with superconducting qubits has not yet been achieved. Here we demonstrate the conversion of a microwave-frequency excitation of a transmon-a type of superconducting qubit-into an optical photon. We achieve this by using an intermediary nanomechanical resonator that converts the electrical excitation of the qubit into a single phonon by means of a piezoelectric interaction3 and subsequently converts the phonon to an optical photon by means of radiation pressure4. We demonstrate optical photon generation from the qubit by recording quantum Rabi oscillations of the qubit through single-photon detection of the emitted light over an optical fibre. With proposed improvements in the device and external measurement set-up, such quantum transducers might be used to realize new hybrid quantum networks2,5 and, ultimately, distributed quantum computers6,7.
Highlights
Microwave-to-optical frequency conversion can be achieved by bulk optical nonlinearities[12]
Using engineered nanomechanical resonators as such intermediary channels has been a promising direction, where pioneering work in the past decade has demonstrated electrical and optical preparation, control and readout of mechanical modes near their quantum ground state[3,16,17]. These demonstrations, together with rapid developments in superconducting quantum circuits[8], have motivated recent experimental efforts to combine electromechanical and optomechanical devices to build a microwave-to-optical quantum transducer[18,19,20,21,22]. This approach has led to impressive conversion efficiencies[23], all demonstrations so far have been limited to classical signals owing to a combination of challenges associated with optically induced or thermal noise, small transduction bandwidths and device integration complexities
We demonstrate the transduction of the microwave-frequency quantum excitations of a superconducting qubit into light at optical telecommunication frequencies, and use an optical fibre link and single-photon detection to register the quantum Rabi oscillations of the qubit
Summary
Mohammad Mirhosseini[1,2,3,5], Alp Sipahigil[1,2,3,5], Mahmoud Kalaee1,2,3,4,5 & Oskar Painter1,2,3,4 ✉. Using engineered nanomechanical resonators as such intermediary channels has been a promising direction, where pioneering work in the past decade has demonstrated electrical and optical preparation, control and readout of mechanical modes near their quantum ground state[3,16,17] These demonstrations, together with rapid developments in superconducting quantum circuits[8], have motivated recent experimental efforts to combine electromechanical and optomechanical devices to build a microwave-to-optical quantum transducer[18,19,20,21,22]. We use a pulsed scheme to coherently transfer the quantum state of the qubit into a nanomechanical mode by a piezoelectric swap operation, and subsequently convert it to the optical domain by using a pulsed laser drive This approach separates electrical and optical parts of the transduction sequence, avoiding the effects of light-induced noise on the superconducting circuitry. We find an overall added noise photon level for the transduction process to be 0.57 ± 0.2, approaching the threshold required for remote entanglement generation of qubits[24]
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