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Quantum Electric Transport Meets Quantum Optics: Josephson Photonics with Strong Charge-Light Coupling – JosePhSCharLi

Submission summary

Photonics and quantum electronics are currently among the fastest developing fields in physics due to their paramount relevance for future information processing, communication, and sensing. These fields deal with two fundamental quanta in nature, namely, photons and charge carriers, bound together according to the theory of quantum electrodynamics. However, a development which explores the quantum optics of quantum conductors has emerged only very recently as a new interdisciplinary field with new prospects in creating and controlling quantum microwave radiation via quantum electronics. Particularly powerful are devices based on the key components of superconducting quantum electrical circuits, namely, dc-voltage biased Josephson junctions (JJ) coupled to microwave resonators. They allow reaching the domain of strong charge-light interaction in combination with a basically perfect conversion of electrical into photonic energy. The goal of this project is to push forward the full potential of this new class of devices by designing new light sources for quantum microwaves and by exploring the passage from weak to strong charge-photon coupling.
The platforms we will use are conceptually related to those developed in circuit Quantum Electrodynamics (cQED), the solid state analog of cavity QED that valued the Nobel Prize in 2012 to Haroche and Wineland. However, in Josephson photonics a dc voltage bias is applied to the junction which allows to address Cooper pair transfer through JJs directly and induce charge-photon coupling far from equilibrium. This regime is particularly useful for fast quantum microwave devices but forms the last gap of knowledge in Josephson physics: the crossover from the conventional Josephson regime, where the superconducting phase difference across the junction is almost a classical variable, to the Coulomb blockade regime, where the transferred charge is almost a good quantum number that evolves via incoherent tunnel events. Quantum mechanically, the phase difference and the number of transferred Cooper pairs form a set of conjugated variables linked by a Heisenberg uncertainty relation. The intermediate regime, where neither phase nor charge are good quantum numbers, has not been investigated in depth, neither experimentally nor theoretically, and the full potential of the Josephson effect is not known yet.
Specifically, we will show that the flow of Cooper pairs through a dc biased JJ can be exploited to produce practically useful devices in the form of bright sources of non-classical radiation and amplifiers whose noise temperature approaches the limits allowed by quantum mechanics. After demonstrating the principles at work in the microwave range, we will adapt some of these devices to the THz range. In a complementary effort, we will investigate the quantum to classical transition of JJs whose phase becomes better and better defined as quantum fluctuations of the transferred charge increase. To do so, we will exploit a particular feature of these devices: They allow detecting both the creation of non-classical photon states and charge current noise properties.
This project brings together the profound expertise of two experimental and one theory group who have already contributed to the field, and, last but not least, already demonstrated their capacity to collaborate.

Project coordination

Daniel ESTÈVE (Commissariat à l'Energie Atomique et aux Energies Alternatives)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

INAC/SPSMS Institut Nanosciences et Cryogénie
Ulm Ulm University
CEA Commissariat à l'Energie Atomique et aux Energies Alternatives

Help of the ANR 338,299 euros
Beginning and duration of the scientific project: February 2017 - 36 Months

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