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Annalen der Physik

Photon–Qubit–Phonon Interactions: Engineering Photon Delocalization in a Rabi Dimer with a Dissipative Bath (Ann. Phys. 12/2018)

Fulu Zheng, Yuyu Zhang, Lu Wang, Yadong Wei, Yang Zhao

Published Dec 1, 2018• 0 citations
Publisher

Abstract

In article number 1800351, Yang Zhao and co-workers adopt the Dirac–Frenkel time-dependent variational principle combined with multiple Davydov D2 ansätze to investigate the dynamical behavior of Rabi dimers with qubits coupled to a phonon bath. Photons can hop between two transmission-line resonators with a tunneling rate J. In each resonator, a qubit interacts with the photon mode with a coupling strength g. Two qubits are also coupled to a common phonon bath with a strength d, which can be used to engineer photon delocalization.

DOI
10.1002/andp.201870045

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In article number 1800351, Yang Zhao and co-workers adopt the Dirac–Frenkel time-dependent variational principle combined with multiple Davydov D2 ansätze to investigate the dynamical behavior of Rabi dimers with qubits coupled to a phonon bath. Photons can hop between two transmission-line resonators with a tunneling rate J. In each resonator, a qubit interacts with the photon mode with a coupling strength g. Two qubits are also coupled to a common phonon bath with a strength d, which can be used to engineer photon delocalization.
Developed originally for the Holstein polaron, the Davydov D1 ansatz is an efficient, yet extremely accurate trial state for time-dependent variation of the spin-boson model [N. Wu, L. Duan, X. Li, and Y. Zhao, J. Chem. Phys. 138, 084111 (2013)]. In this work, the Dirac-Frenkel time-dependent variational procedure utilizing the Davydov D1 ansatz is implemented to study entanglement dynamics of two qubits under the influence of two independent baths. The Ohmic spectral density is used without the Born-Markov approximation or the rotating-wave approximation. In the strong coupling regime finite-time disentanglement is always found to exist, while at the intermediate coupling regime, the entanglement dynamics calculated by Davydov D1 ansatz displays oscillatory behavior in addition to entanglement disappearance and revival.
We investigate multiple photon-assisted Landau–Zener (LZ) transitions in a hybrid circuit quantum electrodynamics device in which each of two interacting transmission-line resonators is coupled to a qubit, and the qubits are driven by periodic driving fields and also coupled to a common phonon mode. The quantum state of the entire composite system is modeled using the multi-D2 Ansatz in combination with the time-dependent Dirac–Frenkel variational principle. Applying a sinusoidal driving field to one of the qubits, this device is an ideal platform to study the photon-assisted LZ transitions by comparing the dynamics of the two qubits. A series of interfering photon-assisted LZ transitions takes place if the photon frequency is much smaller than the driving amplitude. Once the two energy scales are comparable, independent LZ transitions arise and a transition pathway is revealed using an energy diagram. It is found that both adiabatic and nonadiabatic transitions are involved in the dynamics. Used to model environmental effects on the LZ transitions, the common phonon mode coupled to the qubits allows for more available states to facilitate the LZ transitions. An analytical formula is obtained to estimate the short time phonon population and produces results in reasonable agreement with numerical calculations. Equipped with the knowledge of the photon-assisted LZ transitions in the system, we can precisely manipulate the qubit state and successfully generate the qubit dynamics with a square-wave pattern by applying driving fields to both qubits, opening up new venues to manipulate the states of qubits and photons in quantum information devices and quantum computers.
A nonperturbative treatment, the Dirac-Frenkel time-dependent variation is employed to examine dynamics of the Landau-Zener model with both diagonal and off-diagonal qubit-bath coupling using the multiple Davydov trial states. It is shown that steady-state transition probabilities agree with analytical predictions at long times. Landau-Zener dynamics at intermediate times is little affected by diagonal coupling, and is found to be determined by off-diagonal coupling and tunneling between two diabatic states. We investigate effects of bath spectral densities, coupling strengths, and interaction angles on Laudau-Zener dynamics. Thanks to the multiple Davydov trial states, detailed boson dynamics can also be analyzed in Landau-Zener transitions. The results presented here may help provide guiding principles to manipulate the Laudau-Zener transitions in circuit QED architectures by tuning off-diagonal coupling and tunneling strength.
We employ the Dirac-Frenkel variational principle and the multiple Davydov ansatz to study time-dependent fluorescence spectra of a driven qubit in the weak to strong qubit-reservoir coupling regimes, where both the Rabi frequency and the spontaneous decay rate are comparable to the transition frequency of the qubit. Our method agrees well with the time-local master-equation approach in the weak coupling regime, and offers a flexible way to compute the spectra from the bosonic dynamics instead of two-time correlation functions. While the perturbative master equation breaks down in the strong coupling regime, our method actually becomes more accurate due to the use of bosonic coherent states under certain conditions. We show that the counter-rotating coupling between the qubit and the reservoir has considerable contributions to the photon number dynamics and the spectra under strong driving conditions even when the coupling is moderately weak. The time-dependent spectra are found to be generally asymmetric, a feature that is derived from photon number dynamics. In addition, it is shown that the spectral profiles can be dramatically different from the Mollow triplet due to strong dissipation and/or multiphoton processes associated with the strong driving. Our formalism provides a unique perspective to interpret time-dependent spectra.
Abstract Employing the multiple Davydov D 2 Ansätze with the time‐dependent variational principle, photon‐assisted Landau–Zener (LZ) transitions and qubit manipulation in a hybrid quantum electrodynamics device have been investigated. Modeled as a Rabi dimer, the device comprises of two interacting transmission‐line resonators, each coupled to a qubit. The qubits, driven by independent harmonic fields, are further modulated by a micromechanical resonator mimicked by a phonon mode. The impacts of two independent driving fields on the qubit dynamics are carefully examined. The energy diagram of the system and the photon number mobilization on the resonators are analyzed to explain the behavior of the LZ transitions and qubit dynamics while taking into account the influence of the single phonon mode. Results show that low phonon frequencies can alter the qubit dynamics, particularly in the absence of the driving fields, and a strong phonon coupling strength can significantly perturb the qubit dynamics, thanks to a high influx of phonon energy. Notably, only the photon frequency affects the oscillation frequency of qubit polarization. This study unveils the imperative roles that photons and phonons play in the Rabi dimer model.
The quantum Rabi model (QRM), composed of a qubit interacting with a quantized photonic field, is a cornerstone of quantum optics. The QRM with dominant unitary dynamics has been demonstrated in circuit quantum electrodynamics (QED) systems, but an open QRM with a strong photonic dissipation has not been experimentally explored. We here present the first experimental demonstration of such an open system in circuit QED, featuring a controlled competition between the coherent qubit-field interaction and the photonic dissipation. We map out the photon number distributions of the dissipative resonator for different coupling strengths in the steady state. We further observe the variation of the photon number during the system’s evolution toward the steady state with fixed control parameters. The results demonstrate that the system’s behavior is significantly modified by photonic dissipation.