Electro-optic correlations improve an efficient mechanical converter
Andrew P. Higginbotham, Peter S. Burns, Maxwell D. Urmey, Robert W. Peterson, N. S. Kampel, Benjamin Brubaker, Graeme Smith, Konrad W. Lehnert, Cindy A. Regal
An optical network of superconducting quantum bits (qubits) is an appealing platform for quantum communication and distributed quantum computing, but developing a quantum-compatible link between the microwave and optical domains remains an outstanding challenge. Operating at $T < 100$~mK temperatures, as required for quantum electrical circuits, we demonstrate a mechanically-mediated microwave-optical converter with 47$\%$ conversion efficiency, and use a feedforward protocol to reduce added noise to 38~photons. The feedforward protocol harnesses our discovery that noise emitted from the two converter output ports is strongly correlated because both outputs record thermal motion of the same mechanical mode. We also discuss a quantum feedforward protocol that, given high system efficiencies, allows quantum information to be transferred even when thermal phonons enter the mechanical element faster than the electro-optic conversion rate.
An optical network of superconducting quantum bits (qubits) is an appealing platform for quantum communication and distributed quantum computing, but developing a quantum-compatible link between the microwave and optical domains remains an outstanding challenge. Operating at T<100mK temperatures, as required for quantum electrical circuits, we demonstrate a mechanically-mediated microwave-optical converter with 47% conversion efficiency, and use a feedforward protocol to reduce added noise to 38photons. The feedforward protocol harnesses our discovery that noise emitted from the two converter output ports is strongly correlated because both outputs record thermal motion of the same mechanical mode. We also discuss a quantum feedforward protocol that, given high system efficiencies, allows quantum information to be transferred even when thermal phonons enter the mechanical element faster than the electro-optic conversion rate.
The development of scalable quantum networks requires coherent interfaces capable of converting microwave photons used in superconducting quantum processors into optical photons suitable for long-distance fiber transmission. This review surveys recent progress in microwave-to-optical quantum transduction across optomechanical, electro-optic, and magneto-optic platforms, with emphasis on conversion efficiency, bandwidth, added noise, and operating temperature. In addition to standard metrics, we propose the internal efficiency eta_in and the magnon decay rate kappa_m/2pi as normalized parameters that enable fairer comparison across heterogeneous implementations. Optomechanical systems achieve internal phonon-to-photon efficiencies of 93% with sub-quantum added noise of 0.25 quanta at millikelvin temperatures. Electro-optic devices based on LiNbO3 and AlN have advanced from room-temperature efficiencies below 1% to millikelvin systems with internal efficiencies approaching 99.5%, added noise as low as 0.16 quanta at 60 mK, and bandwidths extending to several tens of megahertz. Magneto-optic (optomagnonic) platforms exhibit the lowest efficiencies (typically 10−10 to 10−8), but offer intrinsic non-reciprocity and broadband magnonic operation, with emerging approaches based on topological heterostructures and magnon squeezing predicting enhancements up to 10−4. Optomechanical systems appear promising for high-fidelity quantum state transfer, electro-optic transducers for high-bandwidth coherent links, and magneto-optic devices for non-reciprocal network components. We discuss the fundamental trade-off between efficiency and added noise across all three platforms, and argue that heterogeneous microwave-optical transduction is emerging as a key enabling technology for distributed quantum computing and large-scale quantum networks.
Quantum frequency conversion between superconducting (SC) microwave qubits and telecom optical photons is critical for long distance communication of networked SC quantum processors. While SC qubits operate at cryogenic temperatures to sustain their quantum coherence, converting them to the optical domain enables transferring the quantum states to room temperature and over long distances. For such a quantum state transduction process, several schemes have been investigated, including optomechanics, magnons, piezomechanics, and Pockels electro-optics (EO). The EO conversion approach is particularly attractive since it is broadband, low noise, mechanically and thermally stable (i.e., does not rely on freestanding structures), scalable (largescale integration of EO devices with superconducting circuits is possible), and tunable (e.g., using bias voltages). In this presentation we review our progress in an electro-optic based quantum transduction and discuss the promises and challenges.
State transfer between light and microwaves is a key challenge in quantum networks. Promising transducers use a mechanical intermediary that couples to both fields via radiation pressure. Such electro-optomechanical devices have achieved high efficiencies, yet require resolved-sideband cavities, and generally compromise in scalability and noise performance. Here, we relax this constraint by extending the protocol of Navarathna et al. that transfers optical quantum information onto a mechanical resonator using a broadband, sideband-unresolved cavity and feedback. Combining this with parametric mechanical-to-microwave conversion, we show that continuous optical-to-microwave quantum state transfer is possible using measurement-based feedback, while all-optical coherent feedback enables bidirectional transfer. To assess the transfer, we introduce the quantum transfer witness WT, which -- though similar to the input-referred added noise -- also identifies whether a channel is capable of both preserving Gaussian entanglement and outperforming classical transduction schemes. Finally, we show that quantum-compatible noise performance is within reach of current experimental capabilities. Our results unlock a new design space for electro-optomechanical transducers and strengthens their candidacy as scalable quantum links between distant nodes.
The successes of superconducting quantum circuits at local manipulation of quantum information and photonics technology at long-distance transmission of the same have spurred interest in the development of quantum transducers for efficient, low-noise, and bidirectional frequency conversion of photons between the microwave and optical domains. We propose to realize such functionality through the coupling of electrical, piezoelectric, and optomechanical resonators. The coupling of the mechanical subsystems enables formation of a resonant mechanical supermode that provides a mechanically mediated, efficient single interface to both the microwave and optical domains. The conversion process is analyzed by applying an equivalent circuit model that relates device-level parameters to overall figures of merit for conversion efficiency $\ensuremath{\eta}$ and added noise N. These can be further enhanced by proper impedance matching of the transducer to an input microwave transmission line. The performance of potential transducers is assessed through finite-element simulations, with a focus on geometries in GaAs, followed by considerations of the AlN, LiNbO3, and AlN-on-Si platforms. We present strategies for maximizing $\ensuremath{\eta}$ and minimizing N, and find that simultaneously achieving $\ensuremath{\eta}>50\mathrm{%}$ and N<0.5 should be possible with current technology. We find that the use of a mechanical supermode for mediating transduction is a key enabler for high-efficiency operation, particularly when paired with an appropriate microwave impedance-matching network. Our comprehensive analysis of the full transduction chain enables us to outline a development path for the realization of high-performance quantum transducers that will constitute a valuable resource for quantum information science.
The successes of superconducting quantum circuits at local manipulation of quantum information and photonics technology at long-distance transmission of the same have spurred interest in the development of quantum transducers for efficient, low-noise, and bidirectional frequency conversion of photons between the microwave and optical domains. We propose to realize such functionality through the coupling of electrical, piezoelectric, and optomechanical resonators. The coupling of the mechanical subsystems enables formation of a resonant mechanical supermode that provides a mechanically-mediated, efficient single interface to both the microwave and optical domains. The conversion process is analyzed by applying an equivalent circuit model that relates device-level parameters to overall figures of merit for conversion efficiency η and added noise N. These can be further enhanced by proper impedance matching of the transducer to an input microwave transmission line. The performance of potential transducers is assessed through finite-element simulations, with a focus on geometries in GaAs, followed by considerations of the AlN, LiNbO3, and AlN-on-Si platforms. We present strategies for maximizing η and minimizing N, and find that simultaneously achieving η>50% and N<0.5 should be possible with current technology. Our comprehensive analysis of the full transduction chain enables us to outline a development path for the realization of high-performance quantum transducers that will constitute a new resource for quantum information science.
Converting signals from the microwave to the optical domain has attracted great attention due to its potential applications in the field of quantum networks. Achieving efficient transduction is a significant yet challenging task, where a high efficiency at single photon level and low added noise are required. Electro-opto-mechanics have been proven to be efficient to convert microwave and optical photons bidirectionally. In this work, we propose and demonstrate an enhanced microwave-optical conversion in an electro-opto-mechanical system by introducing a mechanical ancilla attached the microwave resonator. Based on the ancillary electromechanical coupling, the damping rate of the microwave resonator is controlled and further leads to significant enhancement in conversion, such as the increase of conversion efficiency, broadening of conversion bandwidth and reduction of added noise. It provides a feasible approach to realize a broadband microwave-optical conversion with high efficiency. Moreover, the reduced added noise may break the limitation of quantum transduction due to the ancillary electromechanical coupling. Our scheme is also applicable and feasible for opto-mechanics and other systems to achieve practical quantum interface.