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Devices, engines and circuits: quantum engineering with cold atoms

Periodic Reporting for period 3 - DECCA (Devices, engines and circuits: quantum engineering with cold atoms)

Reporting period: 2020-02-01 to 2021-07-31

Understanding quantum systems with many interacting constituents is one of the hardest problem in physics. On the one hand, in most cases it cannot be solved by direct numerical computation, even on the most performant computers in any foreseeable future. On the other hand, such systems are ubiquitous in nature, from materials to electronic devices or even stellar objects such as neutron stars.

In the last decades, a new concept has emerged to observe, control and understand quantum systems using the tools of atomic and optical physics: ensembles of ultra cold atomic gases can be trapped, their interactions controlled so as to mimic a wide range of quantum many-body systems. This ‘quantum simulation’ approach is now one of the most promising direction in many-body physics.

The present project proposes a method to observe the evolution in time of interacting, Fermionic atoms. While quantum mechanics forbids measurements without disturbance, the methods of cavity quantum electrodynamics has allowed to reach the quantum limit for simple systems, such as single atoms. We will extend this method, reaching for this ultimate limit for complex quantum systems with interacting particles, providing a quantum simulation platform with performance only limited by the principles of quantum mechanics. This novel experimental system will be applied to the study of the behavior of nano-electronic devices, and more generally to the quantum simulation of the time evolution of Fermionic quantum systems.
In the first period of the project, we have designed, assembled and tested the experimental setup. The combination of a state-of-the art optical interferometer (the high finesse cavity), with the ability to produce and observe ultra-cold, interacting Fermions had never been realized so far, and most of the efforts have been dedicated to the technical development of this novel platform.

All the tests have been successful, the first Fermionic gas inside an optical cavity has been produced in our laboratory, and its intrinsic properties as well as its coupling with light have been characterized, fitting exactly our expectations. In the mean time, we have performed several theoretical studies, developing experimental protocols for the investigation of transport processes in quantum many-body systems. We have also developed the theory of the operation of our combined Fermi gas - cavity platform, confirming that its performance should reach the quantum limits.

We are now entering the phase where we will make use of the new platform to gather new insights on the physics of complex quantum systems.
In the first phase of the project, we have successfully operated a combined Fermi gas - optical cavity system, which had never been achieved so far. This unique platform provides several opportunities to gather a new understanding and a new level of control over quantum systems.

In the next phase of the project, we will investigate this new combined system. In particular, the question of measurement back-action, which sets the limit to noise and accuracy, will be investigated since the cavity allows in principle to reach it. This will then open the possibility to use the cavity system to look at transport or other dynamic phenomena, where no exact theoretical treatment is possible.

A new idea has emerged recently in the neighboring field of condensed matter physics, where it is proposed to use cavity systems to enhance superconductivity. Our system would provide a way to test these ideas, with the potential of applications for future material science and superconducting technologies.
Artist view of the experimental system developped in the project