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Hybrid Cavity Quantum Electrodynamics with Atoms and Circuits

Final Report Summary - HYBRIDQED (Hybrid Cavity Quantum Electrodynamics with Atoms and Circuits)

Modern micro and nano-electronic circuit technology has reached a stage at which single electric charges, single magnetic flux quanta, single spins and single photons can be isolated, manipulated and detected in integrated electronic circuits. Making use of these fundamental entities for information processing and communication technology is a major driver of current basic research but also attracts more and more attention in industrial settings. Around the world hundreds of academic and industrial labs are investigating novel approaches to make use of the currents flowing in electronic circuits, the quantized magnetic fields generated by those currents, the magnetic structures that are governed by single spins and the radiation that is generated in form of photons. Almost all conventional information and communication technologies are based on using large numbers of these basic physical entities for storing or transferring individual bits of information. However, active research is pursued in our lab and elsewhere towards building the most powerful information processors and the most efficient communication schemes conceivable using individual entities. When working with these individual objects we aim at harnessing their quantum mechanical properties for performing tasks impossible when limited to conventional information processing based on the laws of classical physics.

The HYBRIDQED project addressed this domain of research and development from two different perspectives. In one part of the project we aimed at harnessing the excellent quantum mechanical properties of individual atoms in the context of information processing with electronic circuits. In the second part of the project we developed techniques to generate, manipulate and detect individual microwave frequency photons for use in information technology.

In a very successful range of work we created continuous and pulsed sources of individual microwave photons, the quantum mechanical single entities which we are after. We operated on demand pulsed sources of single photons up to two million times per second. In continuous sources individual photons were created when a large number of photons tried to pass through a device that is reminiscent of a turnstile. We also realized a source in which the individual photons are expected to be efficiently reabsorbed at a quantum mechanical absorber. This is important for establishing quantum communication links on chips, between chips and across larger length scales. For characterizing the properties of individual microwave photons we developed entirely new experimental methods based on measurements of the statistical properties of the amplitude and phase of the weak electromagnetic waves that they create. This technological and scientific achievement is a first of its kind and was further improved remarkably by our own development of quantum limited microwave frequency amplifiers.

We successfully constructed a novel experimental setup in which highly excited atoms, so-called Rydberg atoms, traverse electronic circuits. In these experiments we made use of the outstanding quantum properties of individual atoms and their interaction with electronic circuits for information processing. To preserve the advantageous quantum properties of both the circuit and the atoms at microwave frequencies this apparatus was operated under cryogenic conditions. We demonstrated aspects of the quantum nature of the interaction of the atoms with the circuit in time resolved and spectroscopic measurements. We also used Rydberg atoms as sensors of static and alternating electromagnetic fields emanating from the electronic circuits. These experiments allowed us to learn both about atoms and circuits through their mutual interaction governed by the laws of quantum physics.

In continuing experiments, we decelerate small ensembles or even individual atoms above the electronic circuit, address them, and exchange physical information between the atom and the circuit. The continuation of the project is expected to allow us to harness the mutual interaction of atoms and circuits to process information in novel ways governed by the laws of quantum physics.