Radiative Cooling of a Superconducting Resonator

Abstract

Cooling microwave resonators to near the quantum ground state, crucial for their operation in the quantum regime, is typically achieved by direct device refrigeration to a few tens of millikelvin. However, in quantum experiments that require high operation power such as microwave-to-optics quantum transduction, it is desirable to operate at higher temperatures with non-negligible environmental thermal excitations, where larger cooling power is available. In this Letter, we present a radiative cooling protocol to prepare a superconducting microwave mode near its quantum ground state in spite of warm environment temperatures for the resonator. In this proof-of-concept experiment, the mode occupancy of a 10-GHz superconducting resonator thermally anchored at 1.02 K is reduced to 0.44 ± 0.05 by radiatively coupling to a 70-mK cold load. This radiative cooling scheme allows high-operation-power microwave experiments to work in the quantum regime, and opens possibilities for routing microwave quantum states to elevated temperatures.

Cavity piezo-mechanics for superconducting-nanophotonic quantum interface

“…Moreover, it is possible to radiatively cool a gigahertz mode and suppress its thermal occupancy for quantum operations 47 in spite of a hotter physical temperature of the resonator. We have recently demonstrated such radiative cooling of an "Ouroboros" mode by constructing a cooling channel to a millikelvin cold bath 51,52 . In this work, we focus on the demonstration of coherent M-O photon conversion in our triply resonant POM system; systematic characterization of the noise performance as well as the implementation of radiative cooling is subject to future investigation.…”

“…We show that it is possible to suppress both the microwave and the mechanical added noise to subphoton level even the device is physically in a relatively "hot" environment. This can be realized by implementing the radiative cooling scheme 51,52 with an over-coupled microwave port. In addition, a large C om is needed to suppress the mechanical added noise during the optical-to-microwave photon conversion.…”

Bidirectional interconversion of microwave and light with thin-film lithium niobate

“…We note that the microwave resonator is not at its ground state (thermal photon occupancyn th ∼ 5) in this work. Characterization of ground state conversion will be done either in a dilution refrigerator at millikelvin temperature [40] or through a radiative cooling technique with improved microwave Q [52]. By then, it is feasible to utilize TFLN-based devices for entanglement distribution via the heralded entanglement generation between microwave and optical photons with blue-detuned pump pulses and photon-counting setup [53,54].…”

Robust entanglement of an asymmetric quantum dot molecular system in a Josephson junction

“…Recent years, employing the superconducting qubits and superconducting resonators have improved the exploring of quantum entanglement [31] , [32] , quantum teleportation [33] , [34] and quantum computing [35] , [36] studies. Superconducting qubits namely phase [37] , flux [38] and charge [39] qubits can be connected with microwave [40] , electrical [41] , mechanical [42] , and superconducting [43] resonators.…”