Coupling an Ensemble of Electrons on Superfluid Helium to a Superconducting Circuit

Ge Yang,A Fragner,D I Schuster,L Ocola,D A Czaplewski,G Koolstra,R J Schoelkopf

doi:10.1103/physrevx.6.011031

Ge Yang, A Fragner + Show 5 more

Open Access

https://doi.org/10.1103/physrevx.6.011031

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Abstract

The quantized lateral motional states and the spin states of electrons trapped on the surface of superfluid helium have been proposed as basic building blocks of a scalable quantum computer. Circuit quantum electrodynamics (cQED) allows strong dipole coupling between electrons and a high-Q superconducting microwave resonator, enabling such sensitive detection and manipulation of electron degrees of freedom. Here we present the first realization of a hybrid circuit in which a large number of electrons are trapped on the surface of superfluid helium inside a coplanar waveguide resonator. The high finesse of the resonator allows us to observe large dispersive shifts that are many times the linewidth and make fast and sensitive measurements on the collective vibrational modes of the electron ensemble, as well as the superfluid helium film underneath. Furthermore, a large ensemble coupling is observed in the dispersive regime during experiment, and it shows excellent agreement with our numeric model. The coupling strength of the ensemble to the cavity is found to be >1 MHz per electron, indicating the feasibility of achieving single electron strong coupling.

Highlights

The quantized lateral motional states and the spin states of electrons trapped on the surface of superfluid helium have been proposed as basic building blocks of a scalable quantum computer
We present the first realization of a hybrid circuit in which a large number of electrons are trapped on the surface of superfluid helium inside a coplanar waveguide resonator
Electrons on helium are a promising resource for quantum optics and quantum computing [1,2,3,4]

Summary

INTRODUCTION

Electrons on helium are a promising resource for quantum optics and quantum computing [1,2,3,4]. The circuit QED architecture [21,22] offers a path to new experiments in the quantum regime as well as improving the sensitivity and bandwidth of existing measurements In this hybrid approach, electrons are trapped above an on-chip superconducting microwave resonator. Because the energy of a single photon in the cavity is higher than the thermal bath (ħ ω > kb T), it is possible to conduct quantum optics experiments at the single-photon level This dispersive measurement is conceptually similar to the Sommer-Tanner technique [23], but the use of resonant superconducting circuits at microwave frequencies enables better impedance matching, resulting in faster and more sensitive measurements of small ensembles. The resulting evolution of the dispersive shift agrees excellently with our numerical model

EXPERIMENTAL SETUP AND DETECTION TECHNIQUE

HELIUM DYNAMICS

DISPERSIVE MEASUREMENTS OF ELECTRONS IN A CAVITY