Quantum metrology of low frequency electromagnetic modes with frequency upconverters

Kavli Affiliate: Dale Li

| First 5 Authors: Stephen E. Kuenstner, Elizabeth C. van Assendelft, Saptarshi Chaudhuri, Hsiao-Mei Cho, Jason Corbin

| Summary:

We present the RF Quantum Upconverter (RQU) and describe its application to
quantum metrology of electromagnetic modes between dc and the Very High
Frequency band (VHF) ($lesssim$300MHz). The RQU uses a Josephson
interferometer made up of superconducting loops and Josephson junctions to
implement a parametric interaction between a low-frequency electromagnetic mode
(between dc and VHF) and a mode in the microwave C Band ($sim$ 5GHz),
analogous to the radiation pressure interaction between electromagnetic and
mechanical modes in cavity optomechanics. We analyze RQU performance with
quantum amplifier theory, and show that the RQU can operate as a
quantum-limited op-amp in this frequency range. It can also use non-classical
measurement protocols equivalent to those used in cavity optomechanics,
including back-action evading (BAE) measurements, sideband cooling, and
two-mode squeezing. These protocols enable experiments using dc–VHF
electromagnetic modes as quantum sensors with sensitivity better than the
Standard Quantum Limit (SQL). We demonstrate signal upconversion from low
frequencies to microwave C band using an RQU and show a phase-sensitive gain
(extinction ratio) of $46.9$;dB, which is a necessary step towards the
realization of full BAE.

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