Quantum fluctuations in Josephson conduction: Phase slips and charging effects

Superconducting order in a sufficiently narrow and infinitely long wire is destroyed at zero temperature by quantum fluctuations, which induce $2\ensuremath{\pi}$ slips of the phase of the order parameter. However, in a finite-length wire, coherent quantum phase slips would manifest themselves simply as shifts of energy levels in the excitation spectrum of an electrical circuit incorporating this wire. The higher the phase slips' probability amplitude, the larger are the shifts. Phase slips occurring at different locations along the wire interfere with each other. Due to the Aharonov-Casher effect, the resulting full amplitude of a phase slip depends on the offset charges surrounding the wire. Slow temporal fluctuations of the offset charges make the phase-slip amplitudes random functions of time, and therefore turn energy level shifts into linewidths. We experimentally observed this effect on a long Josephson junction array acting as a ``slippery'' wire. The slip-induced linewidths, despite being only of order $100\phantom{\rule{0.28em}{0ex}}\phantom{\rule{4pt}{0ex}}\mathrm{kHz}$ , were resolved from the flux-dependent dephasing of the fluxonium qubit.Superconducting order in a sufficiently narrow and infinitely long wire is destroyed at zero temperature by quantum fluctuations, which induce $2\ensuremath{\pi}$ slips of the phase of the order parameter. However, in a finite-length wire, coherent quantum phase slips would manifest themselves simply as shifts of energy levels in the excitation spectrum of an electrical circuit incorporating this wire. The higher the phase slips' probability amplitude, the larger are the shifts. Phase slips occurring at different locations along the wire interfere with each other. Due to the Aharonov-Casher effect, the resulting full amplitude of a phase slip depends on the offset charges surrounding the wire. Slow temporal fluctuations of the offset charges make the phase-slip amplitudes random functions of time, and therefore turn energy level shifts into linewidths. We experimentally observed this effect on a long Josephson junction array acting as a ``slippery'' wire. The slip-induced linewidths, despite being only of order $100\phantom{\rule{0.28em}{0ex}}\phantom{\rule{4pt}{0ex}}\mathrm{kHz}$, were resolved from the flux-dependent dephasing of the fluxonium qubit.

arXiv:1012.1928Physical Review BJan 11, 2012130 citations

Effect of disorder on coherent quantum phase slips in Josephson junction chains

Aleksandr E. Svetogorov, D. M. Basko

We study coherent quantum phase slips in a Josephson junction chain, including two types of quenched disorder: random spatial modulation of the junction areas and random induced background charges. Usually, the quantum phase-slip amplitude is sensitive to the normal-mode structure of superconducting phase oscillations in the ring (Mooij-Sch\"on modes, which are all localized by the area disorder). However, we show that the modes' contribution to the disorder-induced phase-slip action fluctuations is small, and the fluctuations of the action on different junctions are mainly determined by the local junction parameters. We study the statistics of the total quantum phase-slip amplitude on the chain and show that it can be non-Gaussian for not sufficiently long chains.We study coherent quantum phase slips in a Josephson junction chain, including two types of quenched disorder: random spatial modulation of the junction areas and random induced background charges. Usually, the quantum phase-slip amplitude is sensitive to the normal-mode structure of superconducting phase oscillations in the ring (Mooij-Sch\"on modes, which are all localized by the area disorder). However, we show that the modes' contribution to the disorder-induced phase-slip action fluctuations is small, and the fluctuations of the action on different junctions are mainly determined by the local junction parameters. We study the statistics of the total quantum phase-slip amplitude on the chain and show that it can be non-Gaussian for not sufficiently long chains.

arXiv:1806.09501Physical review. B./Physical review. BAug 21, 20183 citations

Squeezing Between Charge and Phase Fluctuations in Small Josephson Junctions.

裕一原田

日本物理學會誌Jan 1, 19960 citations

Suppression of the Josephson current by quantum phase fluctuations: beyond the adiabatic approximation

Ulrich Geigenmüller, Masahito Ueda

Physica B Condensed MatterFeb 1, 19940 citations

100\phantom{\rule{0.28em}{0ex}}\phantom{\rule{4pt}{0ex}}\mathrm{kHz}

, were resolved from the flux-dependent dephasing of the fluxonium qubit.