Abstract
The ability to generate single photons is not only an ubiquitous tool for scientific exploration with applications ranging from spectroscopy and metrology to quantum computing, but also an important proof of the underlying quantum nature of a physical process. In the microwave regime, emission of anti-bunched radiation has so far relied on coherent control of Josephson qubits, where precisely calibrated microwave pulses are needed, and the achievable bandwidth is limited by the anharmonicity of the qubit. Here, we demonstrate the operation of a bright on-demand source of quantum microwave radiation capable of emitting anti-bunched photons based on inelastic Cooper pair tunneling and driven by a simple DC voltage bias. It is characterized by its normalized second order correlation function of $g^{(2)}(0)\approx0.43$ corresponding to anti-bunching in the single photon regime. Our source can be triggered and its emission rate is tunable in situ exceeding rates obtained with current microwave single photon sources by more than one order of magnitude.
Highlights
Josephson photonics has recently emerged as a way to directly generate and manipulate quantum microwaves without the need for complicated microwave control drives [1,2,3,4,5,6,7,8]
We experimentally demonstrate the operation of a bright on-demand source of quantum microwave radiation driven by a simple dc voltage bias across a Josephson junction
Our source is based on photon emission into a microwave resonator through inelastic Cooper pair tunneling regulated by a high-impedance RC circuit preventing simultaneous tunnel events
Summary
Josephson photonics has recently emerged as a way to directly generate and manipulate quantum microwaves without the need for complicated microwave control drives [1,2,3,4,5,6,7,8] It relies on inelastic Cooper pair tunneling where a dc-voltage-biased Josephson tunnel junction can admit a finite direct current, even if the applied bias voltage is smaller than its gap [9]. Ic is the critical current of the junction, Re ZðfÞ is the real part of the impedance describing the electromagnetic environment, and PðhfÞ is the probability density for a tunneling Cooper pair to exchange an energy hf with this environment [9,12]. The present work, as well as Ref. [17], demonstrates a device where the electromagnetic environment of the junction is engineered to create antibunched photon emission, showing quantum statistics generated through inelastic Cooper pair tunneling
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