Aharonov-Casher Effect and the Coherent Flux Tunneling in the Hybrid Charge Quantum Interference Device

Abstract

By exploiting the Aharonov-Casher effect we demonstrate a suppression of magnetic flux tunneling in a Hybrid Charge Quantum Interference Device. The main part of this device is two Josephson junctions with a small superconducting island between them. To minimize phase fluctuations across Josephson junctions, this structure is embedded in a compact super-inductive NbN loop. The Interference between the flux tunneling paths is determined by the island-induced charge, which is controlled by an external voltage. The charge sensitive operation of the device is subjected to poisoning by the quasiparticles generated in the NbN film.

Figures (4)

• Figure 1: (a) A schematic of the sample. The h-CQUID consists of the superconducting loop (venous) interrupted by two Josephson junctions (cyan). A superconducting island (yellow) between the junctions is capacitively coupled to a voltage gate. The h-CQUID shares part of the loop with $\lambda$/2 resonator. (b) A representation of addition and subtraction of phase slip phasors in Josephson junction 1 and 2. The angle between the phasors is $\pi Q/e$. With additional quasiparticle in the island, the total phase slip amplitude becomes $\lvert\nu_1 - \nu_2\rvert$. (c) The SEM image (false colour) of multiple h-CQUIDs coupled to a $\lambda$/2 resonator (venous) and gate electrodes (green). (d) SEM image of a single h-CQUID. The picture has the same colour scheme as (a) and (c).
• Figure 2: Transmission of the NbN line resonator. There are 3 resonance modes in the spectral range of our measurement: 3.671 GHz, 6.670 GHz, 10.676 GHz. Insert: Third mode (blue) at 10.676 GHz is used for two-tone spectroscopy. Dashed red line is the Lorentzian fit. The resonance has a quality factor of $Q\approx$ 520.
• Figure 3: (a) Two-tone spectroscopy of the h-CQUID at different deviation of magnetic flux $\Delta \Phi$ from the degeneracy point. The spectral line is overlaid with white dashed line of equation (\ref{['eq: deltaE']}). The parameters of the fit line are: $I_p$= 11.5 nA, $E_S(Q)$= 2.555 GHz. There are additional spectroscopy lines in the intensity plot (the modes of resonator, different qubits etc.) (b) Rabi oscillations of the qubit taken at the degeneracy point $\Delta \Phi$=0. The relaxation time of qubit $T_1$=20 ns.
• Figure 4: (a) Spectroscopy of the h-CQUID under study at the degeneracy point $\Delta\Phi$=0 taken at different $Q=C_gV_g$. h-CQUID has small asymmetry of JJs, $\nu_1$= 1.48 GHz and $\nu_2$= 1.08 GHz. There are two oscillating curves with even and odd parities of charge. The period of oscillations of individual curve is $2e$. The curves are overlaid with the dashed fitting lines of Eq. \ref{['eq: deltaE']}. (b) Spectroscopy of the h-CQUID with large asymmetry of JJs, $\nu_1$= 3.15 GHz and $\nu_2$= 1.45 GHz.