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Sujet de stage / Master 2 Internship

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Stabilization of a Fock state in a dc biased Josephson junction circuit

Contact: PORTIER Fabien, , fabien.portier@cea.fr, +33 1 69 08 72 16/74 75
We will couple a dc voltage biased Josephson junction to two microwave resonators: a strongly coupled mode and a dump mode with low coupling and short lifetime. If the energy of a Cooper pair transmitted through the junction corresponds to the sum of the energies of a photon in either modes, this stabilizes a single photon Fock state in the stringly coupled mode.
Possibility of continuation in PhD: Oui
Deadline for application:06/04/2018

Full description:
This project belongs to the fast growing field of quantum microwaves with Josephson junction circuits. We wish to show that by astutely designing the electromagnetic environment of a dc biased Josephson junction, one can stabilize a Fock state of a microwave resonator. The device involved in this project is the following: a Josephson junction is coupled to two resonators of frequency ν1,ν2 and biased at a voltage V. As the Josephson junction is a non-dissipative element, a DC current flows through the circuit only if 2eV=n1 hν1+ n2 hν2, so that the energy provided by the generator upon the transfer of a Cooper pair is converted into electromagnetic excitations of the resonators. The purpose of this internship is to demonstrate that this device can be used to stabilize the single photon Fock state in one of the resonators: by increasing the coupling of resonator 1 to the junction, one enters a regime where the transition from |1> to |2> is suppressed. At 2eV = hν1, this blockade doesn’t stabilize the |1> state, as a Cooper pair can tunnel backward, with a transition |1> to |0>. To suppress this possibility, we will use the second mode as a dump mode with a very short lifetime. By setting the voltage at 2eV=hν1+ hν2: a Cooper pair then tunnels through the junction, emitting a photon in both resonators, mode 2 empties quickly, and therefore the back tunneling of a Cooper pair is suppressed by energy conservation, stabilizing the single photon Fock state of resonator 1. The trainee will be involved in all the steps of the experiment: design and fabrication of the sample, using nanolithography, cooling of the sample by a dilution refrigerator, and characterization by ultra-low-noise microwave measurements. All these techniques are well mastered by our group.

1 M. Westig et al., Phys Rev Lett 119, 137001 (2017)
2 P. P. Hofer, J.-R. Souquet, and A. A. Clerk, Phys. Rev. B 93, 041418 (2016)

Technics/methods used during the internship:
Nanofabrication, cryogenics, ultralow noise electronics

Tutor of the internship


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