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

Journal of Physics Conference Series

Observation and calculation of higher-order sideband transitions in a flux qubit coupled to a SQUID-based resonator

Yoshihiro Shimazu, Ryōen Shirasaki, S Toda, H. Yamanashi

Published Dec 8, 2014• 0 citations
Publisher

Abstract

Qubit-resonator coupled systems have been intensively studied because of their potential usefulness in quantum information processing. We investigated a superconducting flux qubit coupled to a resonator mode (SQUID plasma mode) associated with a dc SQUID used to read out the qubit state. Higher-order red and blue sideband transitions with | M | = 1, 2, and 3, where M represents the change in the quantum number of the resonator state, were clearly observed away from the symmetry point. We calculated the transition matrix elements between the dressed states and examined their dependence on both the coupling strength and the flux bias for the qubit. The observation of the sidebands up to | M | = 3 is consistent with the calculation results.

DOI
10.1088/1742-6596/568/5/052030

Related papers

Observation of Higher-Order Sideband Transitions and First-Order Sideband Rabi Oscillations in a Superconducting Flux Qubit Coupled to a SQUID Plasma Mode

Yoshihiro Shimazu, Masaki Takahashi, Natsuki Okamura

We report results of spectroscopic measurements and time-domain measurements of a superconducting flux qubit. The dc superconducting quantum interference device (SQUID), used for readout of the qubit, and a shunt capacitor formed an LC resonator generating a SQUID plasma mode. Higher-order red and blue sidebands were observed in a simple measurement scheme because the resonant energy of the resonator, 600 MHz, was comparable to the thermal energy. We also observed Rabi oscillations on the carrier transition and the first-order sideband transitions. Because the qubit was coupled to a single arm of the dc SQUID, the qubit-SQUID coupling was significant at zero bias current, where these phenomena were observed. The ratios between the Rabi periods for the carrier transition and the sideband transitions are compared with those estimated from the coupling constant, which was separately determined. The result may be explained by assuming initial excitation of the resonator.

arXiv:1305.6159•Journal of the Physical Society of Japan•Jun 14, 2013•3 citations

Control of the transition frequency of a superconducting flux qubit by longitudinal coupling to the photon number degree of freedom in a resonator

Hiraku Toida, Takuya Ohrai, Yuichiro Matsuzaki +2 more

We control the transition frequency of a superconducting flux qubit coupled to a frequency-tunable resonator comprising a direct current superconducting quantum interference device (dc SQUID) by microwave driving. The dc SQUID mediates the coupling between microwave photons in the resonator and a flux qubit. The polarity of the frequency shift depends on the sign of the flux bias for the qubit and can be both positive and negative. The absolute value of the frequency shift becomes larger by increasing the photon number in the resonator. These behaviors are reproduced by a model considering the magnetic interaction between the flux qubit and dc SQUID. The tuning range of the transition frequency of the flux qubit reaches $\ensuremath{\approx}1.9\phantom{\rule{0.16em}{0ex}}\mathrm{GHz}$. The effect of photon number fluctuation in the resonator to the dephasing rate of the flux qubit is also discussed.

arXiv:2005.06155•Physical review. B./Physical review. B•Sep 3, 2020•5 citations

Multifrequency modes in superconducting resonators: Bridging frequency gaps in off-resonant couplings

Christian Kraglund Andersen, Klaus Mølmer

A superconducting quantum interference device (SQUID) inserted in a superconducting waveguide resonator imposes current and voltage boundary conditions that makes it suitable as a tuning element for the resonator modes. If such a SQUID element is subject to a periodically varying magnetic flux, the resonator modes acquire frequency sidebands. In this work we calculate the multifrequency eigenmodes of resonators coupled to periodically driven SQUIDs and we use the Lagrange formalism to propose a theory for their quantization. The elementary excitations of a multifrequency mode can couple resonantly to physical systems with different transition frequencies and this makes the resonator an efficient quantum bus for state transfer and coherent quantum operations in hybrid quantum systems. As an example of the application of our multifrequency modes, we determine their coupling to transmon qubits with different frequencies and we present a bichromatic scheme for entanglement and gate operations.

arXiv:1410.6644•Physical Review A•Feb 23, 2015•23 citations

Gradiometric flux qubits with tunable gap

M. J. Schwarz, Jan Goetz, Z Jiang +3 more

Abstract. For gradiometric three-Josephson-junction flux qubits, we perform a systematic study on the tuning of the minimal transition frequency, the so-called qubit gap. By replacing one of the qubit’s Josephson junctions by a dc SQUID, the critical current of this SQUID and, in turn, the qubit gap can be tuned in situ by a control flux threading the SQUID loop. We present spectroscopic measurements demonstrating a well-defined controllability of the qubit gap between zero and more than 10 GHz. This is important for tuning the qubit into and out of resonance with other superconducting quantum circuits in scalable architectures, while still operating it at its symmetry point with optimal dephasing properties. The experimental data agree very well with model calculations based on the full qubit Hamiltonian. From a numerical fit, we determine the Josephson coupling and the charging energies of the qubit junctions. The derived values agree well with those measured for other junctions fabricated on the same chip. We also demonstrate the biasing of gradiometric flux qubits near the symmetry point by trapping an odd number of flux quanta in the gradiometer loop. In this way, we study the effect of the significant kinetic inductance, thereby obtaining valuable information for the qubit design.

•Aug 17, 2016•36 citations

Single-photon-driven high-order sideband transitions in an ultrastrongly coupled circuit-quantum-electrodynamics system

Zhen Chen, Yimin Wang, Tiefu Li +8 more

We report the experimental observation of high-order sideband transitions at the single-photon level in a quantum circuit system of a flux qubit ultrastrongly coupled to a coplanar waveguide resonator. With the coupling strength reaching 10% of the resonator's fundamental frequency, we obtain clear signatures of higher order red-sideband and first-order blue-sideband transitions, which are mainly due to the ultrastrong Rabi coupling. Our observation advances the understanding of ultrastrongly coupled systems and paves the way to study high-order processes in the quantum Rabi model at the single-photon level.

arXiv:1602.01584•Physical Review A•Jul 19, 2017•113 citations

rf-SQUID-Mediated Coherent Tunable Coupling between a Superconducting Phase Qubit and a Lumped-Element Resonator

Michael S. Allman, Fabio Altomare, Jed D. Whittaker +6 more

We demonstrate coherent tunable coupling between a superconducting phase qubit and a lumped-element resonator. The coupling strength is mediated by a flux-biased rf SQUID operated in the nonhysteretic regime. By tuning the applied flux bias to the rf SQUID we change the effective mutual inductance, and thus the coupling energy, between the phase qubit and resonator. We verify the modulation of coupling strength from 0 to 100 MHz by observing modulation in the size of the splitting in the phase qubit's spectroscopy, as well as coherently by observing modulation in the vacuum Rabi oscillation frequency when on resonance. The measured spectroscopic splittings and vacuum Rabi oscillations agree well with theoretical predictions.

arXiv:1001.0816•Physical Review Letters•Apr 29, 2010•89 citations
Qubit-resonator coupled systems have been intensively studied because of their potential usefulness in quantum information processing. We investigated a superconducting flux qubit coupled to a resonator mode (SQUID plasma mode) associated with a dc SQUID used to read out the qubit state. Higher-order red and blue sideband transitions with | M | = 1, 2, and 3, where M represents the change in the quantum number of the resonator state, were clearly observed away from the symmetry point. We calculated the transition matrix elements between the dressed states and examined their dependence on both the coupling strength and the flux bias for the qubit. The observation of the sidebands up to | M | = 3 is consistent with the calculation results.
We report results of spectroscopic measurements and time-domain measurements of a superconducting flux qubit. The dc superconducting quantum interference device (SQUID), used for readout of the qubit, and a shunt capacitor formed an LC resonator generating a SQUID plasma mode. Higher-order red and blue sidebands were observed in a simple measurement scheme because the resonant energy of the resonator, 600 MHz, was comparable to the thermal energy. We also observed Rabi oscillations on the carrier transition and the first-order sideband transitions. Because the qubit was coupled to a single arm of the dc SQUID, the qubit-SQUID coupling was significant at zero bias current, where these phenomena were observed. The ratios between the Rabi periods for the carrier transition and the sideband transitions are compared with those estimated from the coupling constant, which was separately determined. The result may be explained by assuming initial excitation of the resonator.
We control the transition frequency of a superconducting flux qubit coupled to a frequency-tunable resonator comprising a direct current superconducting quantum interference device (dc SQUID) by microwave driving. The dc SQUID mediates the coupling between microwave photons in the resonator and a flux qubit. The polarity of the frequency shift depends on the sign of the flux bias for the qubit and can be both positive and negative. The absolute value of the frequency shift becomes larger by increasing the photon number in the resonator. These behaviors are reproduced by a model considering the magnetic interaction between the flux qubit and dc SQUID. The tuning range of the transition frequency of the flux qubit reaches $\ensuremath{\approx}1.9\phantom{\rule{0.16em}{0ex}}\mathrm{GHz}$. The effect of photon number fluctuation in the resonator to the dephasing rate of the flux qubit is also discussed.
A superconducting quantum interference device (SQUID) inserted in a superconducting waveguide resonator imposes current and voltage boundary conditions that makes it suitable as a tuning element for the resonator modes. If such a SQUID element is subject to a periodically varying magnetic flux, the resonator modes acquire frequency sidebands. In this work we calculate the multifrequency eigenmodes of resonators coupled to periodically driven SQUIDs and we use the Lagrange formalism to propose a theory for their quantization. The elementary excitations of a multifrequency mode can couple resonantly to physical systems with different transition frequencies and this makes the resonator an efficient quantum bus for state transfer and coherent quantum operations in hybrid quantum systems. As an example of the application of our multifrequency modes, we determine their coupling to transmon qubits with different frequencies and we present a bichromatic scheme for entanglement and gate operations.
Abstract. For gradiometric three-Josephson-junction flux qubits, we perform a systematic study on the tuning of the minimal transition frequency, the so-called qubit gap. By replacing one of the qubit’s Josephson junctions by a dc SQUID, the critical current of this SQUID and, in turn, the qubit gap can be tuned in situ by a control flux threading the SQUID loop. We present spectroscopic measurements demonstrating a well-defined controllability of the qubit gap between zero and more than 10 GHz. This is important for tuning the qubit into and out of resonance with other superconducting quantum circuits in scalable architectures, while still operating it at its symmetry point with optimal dephasing properties. The experimental data agree very well with model calculations based on the full qubit Hamiltonian. From a numerical fit, we determine the Josephson coupling and the charging energies of the qubit junctions. The derived values agree well with those measured for other junctions fabricated on the same chip. We also demonstrate the biasing of gradiometric flux qubits near the symmetry point by trapping an odd number of flux quanta in the gradiometer loop. In this way, we study the effect of the significant kinetic inductance, thereby obtaining valuable information for the qubit design.
We report the experimental observation of high-order sideband transitions at the single-photon level in a quantum circuit system of a flux qubit ultrastrongly coupled to a coplanar waveguide resonator. With the coupling strength reaching 10% of the resonator's fundamental frequency, we obtain clear signatures of higher order red-sideband and first-order blue-sideband transitions, which are mainly due to the ultrastrong Rabi coupling. Our observation advances the understanding of ultrastrongly coupled systems and paves the way to study high-order processes in the quantum Rabi model at the single-photon level.
We demonstrate coherent tunable coupling between a superconducting phase qubit and a lumped-element resonator. The coupling strength is mediated by a flux-biased rf SQUID operated in the nonhysteretic regime. By tuning the applied flux bias to the rf SQUID we change the effective mutual inductance, and thus the coupling energy, between the phase qubit and resonator. We verify the modulation of coupling strength from 0 to 100 MHz by observing modulation in the size of the splitting in the phase qubit's spectroscopy, as well as coherently by observing modulation in the vacuum Rabi oscillation frequency when on resonance. The measured spectroscopic splittings and vacuum Rabi oscillations agree well with theoretical predictions.