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:1109.1305 · Physica Scripta

Validity of resonant two-qubit gates in the ultrastrong coupling regime of circuit quantum electrodynamics

Y M Wang, D Ballester, G Romero, V Scarani, E Solano

Published Feb 1, 2012• 9 citations
arXivHTMLPDF

Abstract

We investigate theoretically the performance of resonant two-qubit gates in the crossover from the strong to the ultrastrong coupling regime of light–matter interaction in circuit quantum electrodynamics. Two controlled-phase (CPHASE) gate schemes—which work well within the rotating wave-approximation—are analysed while taking into account the effects of counter-rotating terms appearing in the Hamiltonian. Our numerical results show that the fidelity of the gate operation is above 96% when the ratio between the coupling strength and the resonator frequency, g / ω r , is about 10%. Novel schemes are required in order to implement ultrafast quantum gates when increasing the ratio g / ω r .

DOI
10.1088/0031-8949/2012/t147/014031

Related papers

Ultrafast Quantum Gates in Circuit QED

Guillermo Romero, Daniel Ballester, Yimin Wang +2 more

We present a method to implement ultrafast two-qubit gates valid for the ultrastrong coupling and deep strong coupling regimes of light-matter interaction, considering state-of-the-art circuit quantum electrodynamics technology. Our proposal includes a suitable qubit architecture and is based on a four-step sequential displacement of the intracavity field, operating at a time proportional to the inverse of the resonator frequency. Through ab initio calculations, we show that these quantum gates can be performed at subnanosecond time scales while keeping a fidelity above 99%.

arXiv:1110.0223•Physical Review Letters•Mar 19, 2012•217 citations

Ultrafast quantum computation in ultrastrongly coupled circuit QED systems

Yimin Wang, Chu Guo, Guo-Qiang Zhang +2 more

The latest technological progress of achieving the ultrastrong-coupling regime in circuit quantum electrodynamics (QED) systems has greatly promoted the developments of quantum physics, where novel quantum optics phenomena and potential computational benefits have been predicted. Here, we propose a scheme to accelerate the nontrivial two-qubit phase gate in a circuit QED system, where superconducting flux qubits are ultrastrongly coupled to a transmission line resonator (TLR), and two more TLRs are coupled to the ultrastrongly-coupled system for assistant. The nontrivial unconventional geometric phase gate between the two flux qubits is achieved based on close-loop displacements of the three-mode intracavity fields. Moreover, as there are three resonators contributing to the phase accumulation, the requirement of the coupling strength to realize the two-qubit gate can be reduced. Further reduction in the coupling strength to achieve a specific controlled-phase gate can be realized by adding more auxiliary resonators to the ultrastrongly-coupled system through superconducting quantum interference devices. We also present a study of our scheme with realistic parameters considering imperfect controls and noisy environment. Our scheme possesses the merits of ultrafastness and noise-tolerance due to the advantages of geometric phases.

Scientific Reports•Mar 10, 2017•32 citations

Counter-rotating effect on frequency shift of flux qubit in ultrastrongly coupled circuit-quantum-electrodynamics system

Zhen Chen, Shuai-Peng Wang, Tiefu Li +1 more

In recent years, quantum Rabi model has aroused considerable interest because of its fundamental importance and potential applications in quantum technologies. For a conventional cavity-quantum-electrodynamic (cavity-QED) system involving the interaction between an atom and photons in a cavity, the atom-photon coupling frequency is much smaller than the transition frequency of the atom and the frequency of the cavity mode. This cavity-QED system is usually described by the Jaynes-Cummings model in which the rotating-wave approximation can be adopted by neglecting the counter-rotating coupling terms in the Hamiltonian of the system. However, by designing the unique structure of the superconducting circuit, the ultrastrong-coupling regime can be achieved in a circuit-QED system in which the counter-rotating coupling terms become as important as the rotating terms. Thus, the rotating-wave approximation cannot be used in the ultrastrongly coupled circuit-QED system. Owing to the ultrastrong coupling, this circuit-QED system is described by the standard quantum Rabi model when a superconducting qubit is coupled only to a single resonator mode. In this work, we experimentally study an ultrastrongly coupled circuit-QED system consisting of a four-junction superconducting flux qubit and a muti-mode coplanar-waveguide resonator. The transmission-spectrum measurement and numerical simulations show that the system is in the ultrastrong-coupling regime. By changing the photon number in the resonator, we observe the frequency shift of the flux qubit via the spectroscopic measurement. This frequency shift contains the contributions from not only the rotating-coupling terms but also the counter-rotating terms, which is in good agreement with the theory. The result indicates that this ultrastrongly-coupled quantum system can be used as a good platform to investigate the quantum Rabi model and has potential applications in various aspects of quantum technology, such as quantum simulation, ultrafast quantum gates, entangled-state preparation and protected qubits.

Acta Physica Sinica•Jan 1, 2020•0 citations

Generation of Dicke states in the ultrastrong-coupling regime of circuit QED systems

Chunfeng Wu, Chu Guo, Yimin Wang +3 more

Ultrastrong coupling in circuit quantum electrodynamics makes enhanced fast quantum operations possible. We present a scheme to realize controllable qubit-resonator interactions in ultrastrong circuit quantum electrodynamics with the aid of a unitary transformation. The controllable qubit-resonator interaction is just one type of the so-called selective resonant interactions. From the effective dynamics, it is possible to create the multipartite Dicke states at nanoseconds with high fidelity if the large detuning constraint of the selective resonant interaction is fulfilled. We also investigate the performance of our scheme in the presence of decoherence. Our results present a promising way toward achieving enhanced fast generation of the Dicke states.

Physical Review A•Jan 27, 2017•40 citations

Ultrastrong-coupling regime of nondipolar light-matter interactions

Simone Felicetti, Myung-Joong Hwang, Alexandre Le Boité

We present a circuit-QED scheme which makes it possible to reach the ultrastrong-coupling regime of a nondipolar interaction between a single qubit and a quantum resonator. We show that the system Hamiltonian is well approximated by a two-photon quantum Rabi model and propose a simple scattering experiment to probe its fundamental properties. In particular, we identify a driving scheme that reveals the change in selection rules characterizing the breakdown of the rotating-wave approximation and the transition from strong to ultrastrong two-photon interactions. Finally, we show that a frequency crowding in a narrow spectral region is observable in the output fluorescence spectrum as the coupling strength approaches the collapse point, paving the way to the direct observation of the onset of the spectral collapse in a solid-state device.

arXiv:1807.02434•Physical Review A•Nov 29, 2018•73 citations

Ultrastrong Jaynes-Cummings model

Jin‐Feng Huang, Jie‐Qiao Liao, Le‐Man Kuang

We propose a reliable scheme to realize the ultrastrong Jaynes-Cummings (JC) model by simultaneously modulating the resonance frequencies of the two-level system and the bosonic mode in the ultrastrong quantum Rabi model. We find that in both the high- and low-frequency modulation regimes, the counter-rotating terms can be completely suppressed without reducing the coupling strength of the rotating-wave terms, and hence the ultrastrong JC Hamiltonian is achieved. The ultrastrong JC interaction can not only be used to implement ultrafast quantum operations such as ultrafast quantum state transfer and quantum logic gates but also will open up a new route to the demonstration of quantum phase transition associated with the JC Hamiltonian across the deep-strong-coupling point. Some discussions on the experimental implementation of this scheme with circuit-QED systems are presented.

arXiv:1902.05779•Physical Review A•Apr 27, 2020•39 citations
We investigate theoretically the performance of resonant two-qubit gates in the crossover from the strong to the ultrastrong coupling regime of light–matter interaction in circuit quantum electrodynamics. Two controlled-phase (CPHASE) gate schemes—which work well within the rotating wave-approximation—are analysed while taking into account the effects of counter-rotating terms appearing in the Hamiltonian. Our numerical results show that the fidelity of the gate operation is above 96% when the ratio between the coupling strength and the resonator frequency, g / ω r , is about 10%. Novel schemes are required in order to implement ultrafast quantum gates when increasing the ratio g / ω r .
We present a method to implement ultrafast two-qubit gates valid for the ultrastrong coupling and deep strong coupling regimes of light-matter interaction, considering state-of-the-art circuit quantum electrodynamics technology. Our proposal includes a suitable qubit architecture and is based on a four-step sequential displacement of the intracavity field, operating at a time proportional to the inverse of the resonator frequency. Through ab initio calculations, we show that these quantum gates can be performed at subnanosecond time scales while keeping a fidelity above 99%.
The latest technological progress of achieving the ultrastrong-coupling regime in circuit quantum electrodynamics (QED) systems has greatly promoted the developments of quantum physics, where novel quantum optics phenomena and potential computational benefits have been predicted. Here, we propose a scheme to accelerate the nontrivial two-qubit phase gate in a circuit QED system, where superconducting flux qubits are ultrastrongly coupled to a transmission line resonator (TLR), and two more TLRs are coupled to the ultrastrongly-coupled system for assistant. The nontrivial unconventional geometric phase gate between the two flux qubits is achieved based on close-loop displacements of the three-mode intracavity fields. Moreover, as there are three resonators contributing to the phase accumulation, the requirement of the coupling strength to realize the two-qubit gate can be reduced. Further reduction in the coupling strength to achieve a specific controlled-phase gate can be realized by adding more auxiliary resonators to the ultrastrongly-coupled system through superconducting quantum interference devices. We also present a study of our scheme with realistic parameters considering imperfect controls and noisy environment. Our scheme possesses the merits of ultrafastness and noise-tolerance due to the advantages of geometric phases.
In recent years, quantum Rabi model has aroused considerable interest because of its fundamental importance and potential applications in quantum technologies. For a conventional cavity-quantum-electrodynamic (cavity-QED) system involving the interaction between an atom and photons in a cavity, the atom-photon coupling frequency is much smaller than the transition frequency of the atom and the frequency of the cavity mode. This cavity-QED system is usually described by the Jaynes-Cummings model in which the rotating-wave approximation can be adopted by neglecting the counter-rotating coupling terms in the Hamiltonian of the system. However, by designing the unique structure of the superconducting circuit, the ultrastrong-coupling regime can be achieved in a circuit-QED system in which the counter-rotating coupling terms become as important as the rotating terms. Thus, the rotating-wave approximation cannot be used in the ultrastrongly coupled circuit-QED system. Owing to the ultrastrong coupling, this circuit-QED system is described by the standard quantum Rabi model when a superconducting qubit is coupled only to a single resonator mode. In this work, we experimentally study an ultrastrongly coupled circuit-QED system consisting of a four-junction superconducting flux qubit and a muti-mode coplanar-waveguide resonator. The transmission-spectrum measurement and numerical simulations show that the system is in the ultrastrong-coupling regime. By changing the photon number in the resonator, we observe the frequency shift of the flux qubit via the spectroscopic measurement. This frequency shift contains the contributions from not only the rotating-coupling terms but also the counter-rotating terms, which is in good agreement with the theory. The result indicates that this ultrastrongly-coupled quantum system can be used as a good platform to investigate the quantum Rabi model and has potential applications in various aspects of quantum technology, such as quantum simulation, ultrafast quantum gates, entangled-state preparation and protected qubits.
Ultrastrong coupling in circuit quantum electrodynamics makes enhanced fast quantum operations possible. We present a scheme to realize controllable qubit-resonator interactions in ultrastrong circuit quantum electrodynamics with the aid of a unitary transformation. The controllable qubit-resonator interaction is just one type of the so-called selective resonant interactions. From the effective dynamics, it is possible to create the multipartite Dicke states at nanoseconds with high fidelity if the large detuning constraint of the selective resonant interaction is fulfilled. We also investigate the performance of our scheme in the presence of decoherence. Our results present a promising way toward achieving enhanced fast generation of the Dicke states.
We present a circuit-QED scheme which makes it possible to reach the ultrastrong-coupling regime of a nondipolar interaction between a single qubit and a quantum resonator. We show that the system Hamiltonian is well approximated by a two-photon quantum Rabi model and propose a simple scattering experiment to probe its fundamental properties. In particular, we identify a driving scheme that reveals the change in selection rules characterizing the breakdown of the rotating-wave approximation and the transition from strong to ultrastrong two-photon interactions. Finally, we show that a frequency crowding in a narrow spectral region is observable in the output fluorescence spectrum as the coupling strength approaches the collapse point, paving the way to the direct observation of the onset of the spectral collapse in a solid-state device.
We propose a reliable scheme to realize the ultrastrong Jaynes-Cummings (JC) model by simultaneously modulating the resonance frequencies of the two-level system and the bosonic mode in the ultrastrong quantum Rabi model. We find that in both the high- and low-frequency modulation regimes, the counter-rotating terms can be completely suppressed without reducing the coupling strength of the rotating-wave terms, and hence the ultrastrong JC Hamiltonian is achieved. The ultrastrong JC interaction can not only be used to implement ultrafast quantum operations such as ultrafast quantum state transfer and quantum logic gates but also will open up a new route to the demonstration of quantum phase transition associated with the JC Hamiltonian across the deep-strong-coupling point. Some discussions on the experimental implementation of this scheme with circuit-QED systems are presented.