Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:cond-mat/0311458 · Physical Review B

dc measurements of macroscopic quantum levels in a superconducting qubit structure with a time-ordered meter

Donald S. Crankshaw, K. Segall, D. Nakada, Terry P. Orlando, Leonid S Levitov, Seth Lloyd, Sergio O. Valenzuela, Nina Marković, M. Tinkham, Karl K. Berggren

Published Apr 1, 2004• 10 citations
arXivHTMLPDF

Abstract

dc measurements are made in a superconducting, persistent current qubit structure with a time-ordered meter. The persistent-current qubit has a double-well potential, with the two minima corresponding to magnetization states of opposite sign. Macroscopic resonant tunneling between the two wells is observed at values of energy bias that correspond to the positions of the calculated quantum levels. The magnetometer, a superconducting quantum interference device, detects the state of the qubit in a time-ordered fashion, measuring one state before the other. This results in a different meter output depending on the initial state, providing different signatures of the energy levels for each tunneling direction.

DOI
10.1103/physrevb.69.144518

Related papers

Impact of time-ordered measurements of the two states in a niobium superconducting qubit structure

K. Segall, Donald S. Crankshaw, D. Nakada +7 more

Measurements of thermal activation are made in a superconducting, niobium persistent-current qubit structure, which has two stable classical states of equal and opposite circulating current. The magnetization signal is read out by ramping the bias current of a dc superconducting quantum interference device. This ramping causes time-ordered measurements of the two states, where measurement of one state occurs before the other. This time ordering results in effective measurement time, which can be used to probe the thermal activation rate between the two states. Fitting the magnetization signal as a function of temperature and ramp time allows one to estimate a quality factor of $3\ifmmode\times\else\texttimes\fi{}{10}^{5}$ for our devices, a value favorable for the observation of long quantum coherence times at lower temperatures.

arXiv:cond-mat/0302553•Physical review. B, Condensed matter•Jun 27, 2003•11 citations

Macroscopic quantum superposition of current states in a Josephson-junction loop

Frank K. Wilhelm, Caspar H. van der Wal, A. C. J. ter Haar +5 more

Abstract. Superconducting circuits with Josephson tunnel junctions are interesting systems for research on quantummechanical behavior of macroscopic degrees of freedom. A particular realization is a small superconducting loop containing three Josephson junctions. Close to magnetic frustration 1=2, the physics of this system corresponds to a double well, whose minima correspond to persistent currents of opposite sign. We present DC measurements of the flux indicating a smooth transition close to the degeneracy point even at very low temperatures. Furthermore, microwavespectroscopy experiments allow for the excitation to the next excited state. The dependence of the energy of the resonance on the applied flux clearly indicates the nature of these states as tunneling-splitted superpositions of flux states. We theoretically analyze the system using a generalized master-equation formulation of the spin-boson model. We address the nature of the measuring process by a switching DC SQUID and the possible interpretation of the spectroscopy data in terms of quantum coherence. We discuss these aspects in the context of further applications as a quantum bit.

Physics-Uspekhi•Oct 1, 2001•4 citations

Observation of Resonant Tunneling between Macroscopically Distinct Quantum Levels

R. Rouse, Siyuan Han, James E. Lukens

We report the first observation of resonant tunneling of a system between two macroscopically distinct states: energy levels in different fluxoid wells of a weakly damped superconducting quantum interference device which differ in mean current by approximately 6 \ensuremath{\mu}A. Near 50 mK, the tunneling rate $\ensuremath{\gamma}({\ensuremath{\Phi}}_{x})$ from the metastable well vs applied flux ${\ensuremath{\Phi}}_{x}$ is found to exhibit a series of local maxima where the levels (spaced by $\ensuremath{\approx}1.9$ K) in the two wells cross. The positions of these maxima agree well with the level crossings calculated using independently determined system parameters.

Physical Review Letters•Aug 21, 1995•206 citations

Nanosecond quantum state detection in a current-biased dc SQUID

Julien Claudon, Aurélien Fay, Emile Hoskinson +1 more

This paper presents our procedure to measure the quantum state of a dc superconducting quantum interference device (SQUID) within a few nanoseconds, using an adiabatic dc flux pulse. Detection of the ground state is governed by standard macroscopic quantum tunneling (MQT) theory, with a small correction due to residual noise in the bias current. In the two-level limit, where the SQUID constitutes a phase qubit, an observed contrast of 0.54 indicates a significant loss in contrast compared to the MQT prediction. It is attributed to spurious depolarization (loss of excited state occupancy) during the leading edge of the adiabatic flux measurement pulse. We give a simple phenomenological relaxation model which is able to predict the observed contrast of multilevel Rabi oscillations for various microwave amplitudes.

arXiv:cond-mat/0702453•Physical Review B•Jul 13, 2007•16 citations

Macroscopic resonant tunneling in an rf-SQUID flux qubit

Shanhua Cong, Yiwen Wang, Guozhu Sun +3 more

We have observed the macroscopic resonant tunneling of magnetic flux between macroscopically distinct quantum states in a superconducting flux qubit. The dependences of the macroscopic resonant tunneling on the barrier height of the potential well, the flux bias and the initial state are investigated. Detailed measurements of the tunneling rate as a function of the flux bias reveal the feature of the quantum noise in the superconducting flux qubit.

Chinese Physics B•May 1, 2011•6 citations

Macroscopic quantum behavior of superconducting quantum interference devices

Maria Gabriella Castellano

Abstract Superconducting quantum interference devices (SQUIDs) are made by a superconducting loop interrupted by one or more Josephson junctions. They are described in terms of a macroscopic variable, the magnetic flux, which shows quantum effects such as tunnelling through a potential barrier. Besides making up the source of a quantum state, SQUIDs also provide the instruments necessary for its probing: as a fact, SQUID based magnetometers have a sensitivity approaching the quantum limit. In this paper I will review the working principle of these devices and illustrate the system of SQUIDs realized in my group to test the quantum behavior at a macroscopic level.

Fortschritte der Physik•Apr 24, 2003•3 citations
dc measurements are made in a superconducting, persistent current qubit structure with a time-ordered meter. The persistent-current qubit has a double-well potential, with the two minima corresponding to magnetization states of opposite sign. Macroscopic resonant tunneling between the two wells is observed at values of energy bias that correspond to the positions of the calculated quantum levels. The magnetometer, a superconducting quantum interference device, detects the state of the qubit in a time-ordered fashion, measuring one state before the other. This results in a different meter output depending on the initial state, providing different signatures of the energy levels for each tunneling direction.
Measurements of thermal activation are made in a superconducting, niobium persistent-current qubit structure, which has two stable classical states of equal and opposite circulating current. The magnetization signal is read out by ramping the bias current of a dc superconducting quantum interference device. This ramping causes time-ordered measurements of the two states, where measurement of one state occurs before the other. This time ordering results in effective measurement time, which can be used to probe the thermal activation rate between the two states. Fitting the magnetization signal as a function of temperature and ramp time allows one to estimate a quality factor of $3\ifmmode\times\else\texttimes\fi{}{10}^{5}$ for our devices, a value favorable for the observation of long quantum coherence times at lower temperatures.
Abstract. Superconducting circuits with Josephson tunnel junctions are interesting systems for research on quantummechanical behavior of macroscopic degrees of freedom. A particular realization is a small superconducting loop containing three Josephson junctions. Close to magnetic frustration 1=2, the physics of this system corresponds to a double well, whose minima correspond to persistent currents of opposite sign. We present DC measurements of the flux indicating a smooth transition close to the degeneracy point even at very low temperatures. Furthermore, microwavespectroscopy experiments allow for the excitation to the next excited state. The dependence of the energy of the resonance on the applied flux clearly indicates the nature of these states as tunneling-splitted superpositions of flux states. We theoretically analyze the system using a generalized master-equation formulation of the spin-boson model. We address the nature of the measuring process by a switching DC SQUID and the possible interpretation of the spectroscopy data in terms of quantum coherence. We discuss these aspects in the context of further applications as a quantum bit.
We report the first observation of resonant tunneling of a system between two macroscopically distinct states: energy levels in different fluxoid wells of a weakly damped superconducting quantum interference device which differ in mean current by approximately 6 \ensuremath{\mu}A. Near 50 mK, the tunneling rate $\ensuremath{\gamma}({\ensuremath{\Phi}}_{x})$ from the metastable well vs applied flux ${\ensuremath{\Phi}}_{x}$ is found to exhibit a series of local maxima where the levels (spaced by $\ensuremath{\approx}1.9$ K) in the two wells cross. The positions of these maxima agree well with the level crossings calculated using independently determined system parameters.
This paper presents our procedure to measure the quantum state of a dc superconducting quantum interference device (SQUID) within a few nanoseconds, using an adiabatic dc flux pulse. Detection of the ground state is governed by standard macroscopic quantum tunneling (MQT) theory, with a small correction due to residual noise in the bias current. In the two-level limit, where the SQUID constitutes a phase qubit, an observed contrast of 0.54 indicates a significant loss in contrast compared to the MQT prediction. It is attributed to spurious depolarization (loss of excited state occupancy) during the leading edge of the adiabatic flux measurement pulse. We give a simple phenomenological relaxation model which is able to predict the observed contrast of multilevel Rabi oscillations for various microwave amplitudes.
Abstract Superconducting quantum interference devices (SQUIDs) are made by a superconducting loop interrupted by one or more Josephson junctions. They are described in terms of a macroscopic variable, the magnetic flux, which shows quantum effects such as tunnelling through a potential barrier. Besides making up the source of a quantum state, SQUIDs also provide the instruments necessary for its probing: as a fact, SQUID based magnetometers have a sensitivity approaching the quantum limit. In this paper I will review the working principle of these devices and illustrate the system of SQUIDs realized in my group to test the quantum behavior at a macroscopic level.