We measured the retrapping current of a small-capacitance underdamped dc superconducting quantum interference device (SQUID) at low temperatures as a function of magnetic field. We found that the relative phase relation between the magnetic-field dependence of the retrapping current and that of the switching current jumped from 0 to $\ensuremath{\pi}$ at ${E}_{\mathrm{J}}\ensuremath{\sim}{E}_{\mathrm{C}},$ where ${E}_{\mathrm{J}}$ and ${E}_{\mathrm{C}}$ are the Josephson energy and the charging energy of a Cooper pair. This phenomenon cannot be reproduced by a model that approximates the SQUID as a single junction with a controllable switching current. It can be explained phenomenologically by taking into account two kinds of dissipation that arise from ac currents flowing through the lead and along the SQUID's loop.We measured the retrapping current of a small-capacitance underdamped dc superconducting quantum interference device (SQUID) at low temperatures as a function of magnetic field. We found that the relative phase relation between the magnetic-field dependence of the retrapping current and that of the switching current jumped from 0 to $\ensuremath{\pi}$ at ${E}_{\mathrm{J}}\ensuremath{\sim}{E}_{\mathrm{C}},$ where ${E}_{\mathrm{J}}$ and ${E}_{\mathrm{C}}$ are the Josephson energy and the charging energy of a Cooper pair. This phenomenon cannot be reproduced by a model that approximates the SQUID as a single junction with a controllable switching current. It can be explained phenomenologically by taking into account two kinds of dissipation that arise from ac currents flowing through the lead and along the SQUID's loop.

Physical review. B, Condensed matterOct 29, 20020 citations

Novel effect of damping circulating currents in DC SQUIDs

Ian Atkin, E. Abraham, Colin M. Pegrum

Czechoslovak Journal of PhysicsMay 1, 19960 citations

Observation of Qubit State with a dc-SQUID and Dissipation Effect in the SQUID

Hideaki Takayanagi, Hirotaka Tanaka, Shiro Saito +1 more

Two states of a flux qubit with three Josephson junctions were shown in a single measurement with a dc-SQUID. The qubit is an aluminum superconductor loop surrounded by a dc-SQUID for readout. It has two states, which have persistent currents flowing in opposite directions. The readout data for three samples with different junction sizes suggest that the probability distribution for the double-well potential depends on the ratio of E J / E C , where E J is the Josephson energy and E C is the charging energy. The probability distribution was estimated by calculating the wavefunctions and energy levels for the measured samples. We measured the retrapping current of a dc-SQUID without the qubit as a function of the magnetic field. It was found that the relative phase relation for the magnetic field dependence of the retrapping current jumped from 0 to π at E J ≈ E C . This jump can be explained phenomenologically by taking into account the two kinds of dissipation arising from ac currents flowing through the lead and along the SQUID loop. The fact that the jump occurred at E J ≈ E C strongly suggests that the quantum nature of the electromagnetic environment needs to be taken into account in order to understand the origin of the dissipation.Two states of a flux qubit with three Josephson junctions were shown in a single measurement with a dc-SQUID. The qubit is an aluminum superconductor loop surrounded by a dc-SQUID for readout. It has two states, which have persistent currents flowing in opposite directions. The readout data for three samples with different junction sizes suggest that the probability distribution for the double-well potential depends on the ratio of E J / E C , where E J is the Josephson energy and E C is the charging energy. The probability distribution was estimated by calculating the wavefunctions and energy levels for the measured samples. We measured the retrapping current of a dc-SQUID without the qubit as a function of the magnetic field. It was found that the relative phase relation for the magnetic field dependence of the retrapping current jumped from 0 to π at E J ≈ E C . This jump can be explained phenomenologically by taking into account the two kinds of dissipation arising from ac currents flowing through the lead and along the SQUID loop. The fact that the jump occurred at E J ≈ E C strongly suggests that the quantum nature of the electromagnetic environment needs to be taken into account in order to understand the origin of the dissipation.

Physica ScriptaJan 1, 200210 citations

The effects of negative dynamic resistance of DC SQUIDs

Sing-Lin Wu, Ming-Jye Wang, Cheng-Chung Chi

Bulletin of the American Physical SocietyMar 21, 20050 citations

Crossover from Kramers to phase-diffusion switching in moderately damped Josephson junctions

Jaan Männik, Shaoxiong Li, Wei Qiu +4 more

We have measured and propose a model for switching rates in a hysteretic dc superconducting quantum interference device (SQUID) in the regime where phase-diffusion processes start to occur. We show that the switching rates in this regime are smaller than the rates given by Kramers' formula due to retrapping of the Josephson phase. The retrapping process, which is affected by the frequency dependent impedance of the environment of the dc SQUID, leads to a peaked second moment of the switching distribution as a function of temperature. The temperatures where the peaks occur are proportional to the critical current of the dc SQUID.We have measured and propose a model for switching rates in a hysteretic dc superconducting quantum interference device (SQUID) in the regime where phase-diffusion processes start to occur. We show that the switching rates in this regime are smaller than the rates given by Kramers' formula due to retrapping of the Josephson phase. The retrapping process, which is affected by the frequency dependent impedance of the environment of the dc SQUID, leads to a peaked second moment of the switching distribution as a function of temperature. The temperatures where the peaks occur are proportional to the critical current of the dc SQUID.

arXiv:cond-mat/0503729Physical Review BJun 24, 200572 citations

{E}_{\mathrm{J}}

and

{E}_{\mathrm{C}}

are the Josephson energy and the charging energy of a Cooper pair. This phenomenon cannot be reproduced by a model that approximates the SQUID as a single junction with a controllable switching current. It can be explained phenomenologically by taking into account two kinds of dissipation that arise from ac currents flowing through the lead and along the SQUID's loop.