INTRIQ Seminar

Microwave quantum measurement based on inelastic Cooper pair tunneling

Max Hofheinz

Department of Electrical and Computer Engineering & Institut Quantique
Université de Sherbrooke

In superconducting quantum circuits the Josephson junction is the key element because it is the only strongly nonlinear and dissipationless circuit element we know. Usually it is used in the superconducting state where it acts as a nonlinear inductor, for example in Josephson qubits or Josephson parametric amplifiers. But a Josephson junction can also be nonlinear and dissipationless when a non-zero DC voltage below the gap is applied. In this regime a Cooper pair current can flow through the junction when the energy 2eV of a tunneling Cooper pair can be dissipated in the form of photons emitted into one or several modes of the linear circuit in which the junction is embedded [1]. In this inelastic Cooper-pair tunneling regime, dubbed “Josephson photonics”, the junction acts as an active nonlinear element, transforming DC power into microwave radiation, similar to a light emitting diode or LASER diode, but at 5 orders of magnitude lower photon energy. We have tailored this physics into quantum microwave sources, such as a single photon source [2]. In this talk I will show that it can also be used to implement quantum measurement devices such as a quantum limited amplifier [3] or a microwave photo-multiplier [4]. I will show that while these devices tend to be less coherent than their counter parts using the Josephson junction in the zero-voltage state, they still allow for quantum-limited performance, and are best suited for open systems operating at high bandwidth.

[1] Bright Side of the Coulomb Blockade, M. Hofheinz et al. Phys. Rev. Lett. 106, 217005 (2011).
[2] A bright on-demand source of anti-bunched microwave photons based on inelastic Cooper pair tunneling, A. Grimm et al. Phys. Rev. X 9, 021016 (2019).
[3] Near-quantum-limited amplification from inelastic Cooper-pair tunnelling, S. Jebari et al. Nat Electron 1, 223-227 (2018).
[4] Multiplying and detecting propagating microwave photons using inelastic Cooper-pair tunneling J. Leppäkangas et al. Phys. Rev. A 97, 013855 (2018).