We apply a simple analytical method based on unitary transformation to calculate the Bloch-Siegert (BS) shift over entire driving-strength range. In quantitative comparison with numerically exact BS obtained by Floquet formalism as well previous results, we confirm that our calculated results are not only accurate in weak-driving regime but also correct strong-driving limit. intermediate regime, values of nearly same ones. It turns out calculation for is beyond perturbation. Meanwhile,...

We investigate electron transport through a double dot Aharonov-Bohm interferometer coupled to heat bath, which provides not only dephasing source but also non-Markovian memory effects. The distribution of waiting times between subsequent transfers is utilized analyze the unique dynamics, especially at short times. show how coherent oscillations in weak system-bath coupling regime are washed out strong limit, due during propagation electrons interferometer. Intriguingly, we find for an...

Dynamics of the two-spin spin-boson model in presence Ohmic and sub-Ohmic baths is investigated by employing a multitude Davydov D1 trial states, also known as multi-D1 Ansatz. Its accuracy dynamics simulations SBM improved significantly over single Ansatz, especially weak to moderately strong coupling regime. Validity Ansatz for various strengths systematically examined making use deviation vector which quantifies how faithfully state obeys Schrödinger equation. The time evolution...

A controllable low noise current lies at the heart of high-precision measurements in quantum transport and metrology. While previous research dealt with suppression through a tunneling junction or single dot (QD) device, present work investigates inhibition double (DQD) system based on closed-loop feedback control. The unique advantage DQD device is that bidirectional bias can be measured by nearby point contact. However, continuous monitoring states inevitably leads to measurement-induced...

We study the spontaneous emission spectra of a few-level giant atom strongly coupled to one-dimensional waveguide by employing variational and analytical approaches, which are beyond rotating-wave approximation Markovian approximation. show that interference effects due multiple coupling points result in dark lines either two-level or three-level atoms regardless whether there is bound state not. illustrate generation depends on distance between their number. In absence state, can be used...

Abstract The resonance and dynamics of a qubit exposed to strong aperiodic bichromatic field are studied by using periodic counter‐rotating hybridized rotating wave (CHRW) Hamiltonian, which is derived from the original Hamiltonian with unitary transformations under reasonable approximation enables application Floquet theory. It found that consistency between CHRW results numerically exact generalized‐Floquet‐theory (GFT) in valid regime former while widely used rotating‐wave breaks down....

The dynamics of the (sub-)Ohmic spin-boson model under various bath initial conditions is investigated by employing Dirac-Frenkel time-dependent variational approach with multiple Davydov D1 Ansatz in interaction picture. validity our carefully checked comparing results those hierarchy equations motion method. By analyzing features nonequilibrium dynamics, we identify phase diagrams for different conditions. We find that spectral exponent s < sc, there exists a transition from coherent to...

A detailed understanding of the full measurement statistics in experiments is basis for thorough device characterization and advanced applications such as quantum metrology. In this spirit, we investigate conditional counting an electron-spin-resonance pumped dot (QD), which tunnel-coupled to a side electrode continuously monitored by point contact (QPC). For noninvasive detector, find that spin current through QD its related cumulants exhibit intriguing features system parameter dependences...

We examine the applicability of numerically accurate method time dependent variation with multiple Davydov Ansätze (mDA) to non-Hermitian systems. As illustrative examples, three systems interest have been studied, a system dissipative Landau-Zener transitions, multimode Jaynes-Cummings model, and Holstein-Tavis-Cummings all which are shown be effectively described by mDA method. Our findings highlight versatility as powerful numerical tool for investigating complex many-body systems, can...

We theoretically study the dynamics and resonance shift of Rabi model with frequency modulation, i.e., driven additionally by a slow longitudinal field, using counterrotating-hybridized rotating-wave (CHRW) method, aiming to illustrate effects counterrotating (CR) terms transverse field. The CHRW method is based on unitary transformation reduces aperiodic Hamiltonian an effective periodic that can be efficiently treated Floquet theory. validity widely used approximation (RWA) carefully...

We investigate the fluorescence spectrum of a two-level system driven by monochromatic classical field Born-Markovian master equation based on unitary transformation. The main purpose is to understand effects counter-rotating-wave terms driving spectral features fluorescence. have derived an analytical expression for spectrum, which different from Mollow's theory, while result resonance limiting case ours in moderately weak regimes. Our results demonstrate precisely that play important role...

We investigate the bias-modulated dynamics of a strongly driven two-level system using counter-rotating-hybridized rotating-wave (CHRW) method. This CHRW method treats driving field and bias on equal footing by unitary transformation with two parameters $\xi$ $\zeta$, is nonperturbative in strength, tunneling amplitude or bias. In addition, this beyond traditional approximation (Rabi-RWA) yet properly choosing transformed Hamiltonian takes RWA form renormalized energy splitting strength. The...

We employ the Dirac-Frenkel variational principle and multiple Davydov ansatz to study time-dependent fluorescence spectra of a driven qubit in weak strong qubit-reservoir coupling regimes, where both Rabi frequency spontaneous decay rate are comparable transition qubit. Our method agrees well with time-local master-equation approach regime, offers flexible way compute from bosonic dynamics instead two-time correlation functions. While perturbative master equation breaks down our actually...

We investigate the pairwise thermal quantum discord in a three-qubit XXZ model with Dzyaloshinskii—Moriya (DM) interaction. find that effects of DM interaction on antiferromagnetic system is distinct from ferromagnetic system. The magnetic field supplemented term contribute to enhance range discord. It revealed situations where fails indicate sudden change groundstate at finite temperature though indicating such zero temperature. Dynamics considered as well. Thermal vanishes asymptotic limit...

We employ a time-dependent variational approach with the multiple Davydov ${D}_{2}$ ansatz and two approximate analytical methods to study spontaneous emission of V-type artificial atom in strong-coupling regime, where decay rate emitter becomes considerable fraction its transition frequencies, focus on quantum-interference-induced effects. The is found be accurate certain regimes used as benchmark address validity methods: rotating-wave approximation (RWA) transformed RWA (TRWA). It that...

We study the fluorescence spectrum from a two-level system with controllable energy separation modulated by longitudinal field and excited transversal field. Combining rotating-wave approximation Floquet theory, we derive formal solution to Bloch equations in presence of both driving fields numerically evaluate spectrum. Exotic spectral features associated added are found be dramatically different standard Mollow triplet multipeak structure. The may experimentally realized context artificial...

We study the dynamics of quantum discord and entanglement for two spin qubits coupled to a chain with Dzyaloshinsky—Moriya interaction. In case two-qubit an initial pure state, correlations decay zero at critical point environment in very short time. mixed it is found that may get maximized due behavior environment, while vanishes under same condition. Besides, we observed sudden transition between classical decoherence when only single qubit interacts environment. The effects interaction on...

We study the origin of symmetry fluorescence spectrum from two-level system subjected to a low-frequency periodic modulation and near-resonant high-frequency monochromatic excitation using analytical numerical methods based on Floquet theory. find that fundamental can be attributed presence generalized parity states, which depends driving parameters. The absence lead asymmetry spectrum. Based parity, conditions for derived, succeeds in predicting harmonic, biharmonic, multiharmonic...

We present a stochastic thermodynamics analysis of an electron-spin-resonance pumped quantum dot device in the Coulomb-blocked regime, where pure spin current is generated without accompanying net charge current. Based on generalized master equation beyond secular approximation, coherences are accounted for terms effective average Floquet basis. Elegantly, this undergoes precession about magnetic field, which originates from non-secular treatment and energy renormalization. It shown that...

We study the vacuum Rabi splitting of a qubit ultrastrongly coupled to high-Q cavity mode and radiation reservoir. Three methods are employed: numerically exact variational approach with multiple Davydov ansatz, rotating-wave approximation (RWA), transformed RWA. Agreement between results RWA is found in regime validity latter, where breaks down completely. illustrate that Lamb shift plays an essential role modifying ultrastrong coupling regime, leading off-resonant qubit-cavity even though...

We use an analytical method to study the dissipative dynamics of a two-level system (TLS) under harmonic driving. The is based on combination unitary transformation and Born--Markov master-equation approach. Our main aim clarify effects counter-rotating (CR) terms both driving TLS-bath (dissipative) coupling dynamics, in comparison with rotating-wave results different schemes, i.e., well-known traditional approximation method, two particular methods: one just takes into account CR other...

We investigate the noise correlations of spin and charge currents through an electron resonance (ESR)-pumped quantum dot, which is tunnel coupled to three electrodes maintained at equivalent chemical potential. A recursive scheme employed with inclusion degrees freedom account for spin-resolved counting statistics in presence non-Markovian effects due coupling a dissipative heat bath. For symmetric spin-up spin-down tunneling rates, ESR-induced flip mechanism generates pure current without...