Population Of Dressed States Research Articles

Dephasing-assisted preparation of asymmetric steering in coupled quantum wells.

It is shown that the dephasing rates are usually harmful for quantum correlations in various systems. Nevertheless, we explore that the dephasing rates in the coupled quantum wells (QWs), as a major contribution of the decay processes, can assist to generate one-way Einstein-Podolsky-Rosen (EPR) steering. By applying two strong fields to drive two dipole-allowed transitions while the other transitions are coupled with two quantized modes, the asymmetric EPR steering is possible to obtain at steady state through a single-pathway dissipation in the three-well system. According to dressed-state and Bogoliubov mode transformation, we find that the dephasing rates play a role in modifying the dressed-state populations and the dissipation rate through multiple quantum interference mechanisms. The positive effect of the dephasing rates from a nanostructure on quantum correlation is expected to find potential applications in quantum information processing.

Manipulation of the asymmetric Einstein–Podolsky–Rosen steering via coherent population transfer

We investigate the Einstein–Podolsky–Rosen (EPR) steering of two cavity modes generated via four-wave mixing processes. For a three-level V-type configuration, a strong coherent field as a dressing field couples the atoms, and a weak coherent field as a control filed resonantly couples one dressed state to the auxiliary state. By using the approach of dressed states and Bogoliubov modes, we find that only one Bogoliubov mode is mediated into the interaction with the dressed atoms, and the other one is decoupled. Due to the presence of the coherent control filed, the channel for dressed state population transfer is established, which plays a key role in the generation of the asymmetric EPR steering of two cavity fields. It is shown that the one-way EPR steering can be manipulated by the Rabi frequencies of the control field and the cooperativity parameters.

Initialization of Single Spin Dressed States using Shortcuts to Adiabaticity.

We demonstrate the use of shortcuts to adiabaticity protocols for initialization, read-out, and coherent control of dressed states generated by closed-contour, coherent driving of a single spin. Such dressed states have recently been shown to exhibit efficient coherence protection, beyond what their two-level counterparts can offer. Our state transfer protocols yield a transfer fidelity of ∼99.4(2)% while accelerating the transfer speed by a factor of 2.6 compared to the adiabatic approach. We show bidirectionality of the accelerated state transfer, which we employ for direct dressed state population read-out after coherent manipulation in the dressed state manifold. Our results enable direct and efficient access to coherence-protected dressed states of individual spins and thereby offer attractive avenues for applications in quantum information processing or quantum sensing.

Quantum control of dressed state population for four-level ladder Li2 molecules in femtosecond laser fields

Using the time-dependent wave packet method, Aulter-Townes splitting in the photoelectron spectra of four-level ladder Li2 molecules is theoretically investigated by two pump and one probe femtosecond laser pulses. Structure of the triple splitting is presented to analyze the information about a selective population of dressed states. It is found that regulating the intensity of laser pulse can control Rabi oscillation and thus tailor the splitting of three peaks. The population and energy of dressed states can be manipulated by changing the wavelength of the second pulse which can be interpreting using doubly dressed states. By adjusting the delay time between pump and probe pulse, one can control the population of the dressed states.

Engineering a squeezed phonon reservoir with a bichromatic driving of a quantum dot

We demonstrate how an acoustic phonon bath when coupled to a quantum dot with the help of a bichromatic laser field may effectively form a quantum squeezed reservoir. This approach allows to achieve an arbitrary degree of squeezing of the effective reservoir and it incorporates the properties of the reservoir into two parameters, which can be controlled by varying the ratio of the Rabi frequencies of the bichromatic field. It is found that for unequal Rabi frequencies, the effective reservoir may appear as a quantum squeezed field of ordinary or inverted harmonic oscillators. When the Rabi frequencies are equal the effective reservoir appears as a perfectly squeezed field in which the decay of one of the polarization quadratures of the quantum dot dipole moment is inhibited. The decay of the quantum dot to a stationary state which depends on the initial coherence is predicted. This unusual result is shown to be a consequence of a quantum-nondemolition type coupling of the quantum dot to the engineered squeezed reservoir. The effect of the initial coherence on the steady-state dressed-state population distribution and the fluorescence spectrum is discussed in details. The complete polarization of the dressed state population and asymmetric spectra composed of only a single Rabi sideband peak are obtained under strictly resonant excitation.

Ensemble of asymmetric quantum dots in a cavity as a terahertz laser source

The possibility of establishing a terahertz laser generation at a transition between the dressed states formed by the interaction of an intense optical field with an ensemble of asymmetric quantum dots (QDs) in a high-Q terahertz cavity is discussed. It has been shown that the population inversion in the system of dressed states is achieved owing to spontaneous relaxation of the excited state of the QDs. The set of Maxwell–Bloch equations for the difference between dressed-state populations, polarization, and population of the cavity mode has been analyzed in the mean-field approximation. The lasing conditions have been clarified and the possibility of controlling the terahertz radiation intensity has been studied, including the case of an inhomogeneously broadened ensemble of QDs.

Quantum control of dressed state population for Li2 molecules by intense femtosecond laser pulses

We investigated the Autler–Townes splitting in photoelectron spectra of molecules steered by ultrashort laser pulses using the time-dependent wave-packet method. Structure of the Autler–Townes splitting was presented to analyze the information of a selective population of the dressed states. It was found that population transfer process, structure of photoelectron spectrum and pattern of Autler–Townes splitting can be controlled by adjusting the intensity, wavelength and delay time of laser pulses.

Ramsey spectroscopy, matter-wave interferometry, and the microwave-lensing frequency shift

We derive the general frequency shift of a microwave atomic clock due to resonant dipole forces acting on the atomic wave functions during the Ramsey interactions. We explicitly demonstrate that only dressed-state populations in position space contribute significantly to the frequency shift and that the de Broglie phases of the dressed-state wave functions do not contribute. In addition, we show that momentum changes in the second Ramsey interaction normally produce negligible frequency shifts in comparison to those from the first Ramsey interaction.

Lasing and phase transition in atomic system with dressed states

The problem of phase transitions in the system of high-density gas of two-level atoms non-resonantly interacting with a pump field in the presence of optical collisions (OCs) and placed in the cavity is studied. The OCs are considered in the framework of thermalization of atomic dressed state (DS) population. For the case of a strong atom-field coupling condition we analyze the problem of thermodynamic equilibrium superradiant phase transition for the order parameter representing real amplitude of cavity mode and taking place as a result of the atomic DS thermalization process. At the same time such a transition can be connected with condensed (coherent) properties of low branch DS-polaritons occurring in the cavity. Various aspects of non-equilibrium phase transition to laser field generation by using atomic DS levels are studied in detail. It is important that for positive atom-light detuning DS lasing can be obtained in the presence of quasi-equilibrium DS population that corresponds to a true two-level atomic system with inversion in perturbative limit.

Quantum control of K2 molecule in an intense laser field：Selective population of dressed states

Control of molecular dynamics in an intense laser field has been studied by employing the time-dependent wave packet approach. A system of K2 molecule in three states (ground state|X, excited state |B and ionized state|X+) serves as a prototype which interacts with pump-probe laser fields. Interacting with an intense pump field, the excited state |B splits into two substates: | and |. Information of the energies and probability distributions of dresses states | and | can be obtained by analysing the photoelectron spectra (PES) of K2 molecule. Meanwhile, the scheme of selective population of dressed states (SPODS) has been put forward according to the dressed states theory of K2 molecule. It is found that regulating the laser intensity can control the dressed state energies, and altering the laser wavelength can make the high selectivity of the dressed state population readied.

Lasing and high-temperature phase transitions in atomic systems with dressed-state polaritons

We consider the fundamental problem of high temperature phase transitions in the system of high density two-level atoms off-resonantly interacting with a pump field in the presence of optical collisions (OCs) and placed in the cavity. OCs are considered in the framework of thermalization of atomic dressed state (DS) population. For the case of a strong atom-field coupling condition we analyze the problem of thermodynamically equilibrium superradiant phase transition for the order parameter representing a real amplitude of cavity mode and taking place as a result of atomic DSs thermalization process. Such transition is also connected with condensed (coherent) properties of low branch (LB) DS-polaritons occurring in the cavity. For describing non-equilibrium phase transitions we derive Maxwell-Bloch like equations which account for cavity decay rate, collisional decay rate and spontaneous emission. Various aspects of transitions to laser field formation by using atomic DS levels for both positive and negative detuning of a pump field from atomic transition frequency are studied in detail. It is revealed, that for positive atom-light detuning DS lasing can be obtained in the presence of quasi-equilibrium DS population that corresponds to a true two-level atomic system with the inversion in nonresonant limit.

Quantum control of a molecular system in an intense field via the selective population of dressed states

We theoretically investigate the physical mechanism of quantum control on a K(2) molecule with an ultrafast strong laser pulse by solving the time-dependent Schrödinger equation exactly using a wave packet approach. The structures of the triple splitting in the 3-photon ionization spectra of a K(2) molecule are presented to analyze the information of a selective population of dressed states. In this work, it is found that the tunability of the dressed states energies is achieved by regulating the laser intensity and the high selectivity of the dressed state population is attained by altering the envelope and wavelength of the intense laser pulse.

Control of resonance fluorescence in coupled quantum dots

Spectral and squeezing properties of the resonance fluorescence of two coupled quantum dots forming an effective Λ-type three-level structure and connected with two normal metal leads are studied. We assume that one of the dots is driven by a strong light field and find that by modulating the bias voltage and the dot-lead coupling strengths, the electron can be selectively trapped in one of the two dressed states produced by the light field. The trapped electron possesses large coherence, and the resulting unbalanced dressed-state populations can lead to a significant enhancement or suppression of the sidebands in the resonance fluorescence spectrum. Moreover, a wideband squeezing can be generated that may be significantly enhanced by modulating the gate voltage.

Squeezing in strong light scattered by a regular structure of atoms

Squeezing in the resonance fluorescence emitted by a regular structure of atoms is discussed. Intense squeezed light fields are a prerequisite, e.g., for efficient measurements with sensitivity below the standard quantum limit. Regular structures are known to offer macroscopic squeezed light due to the fixed phase relation between the light scattered by the respective atoms, but typically restrict squeezing to low incident light intensity. As our main result, we demonstrate that this restriction to low driving field intensity can be circumvented. For this, we assume a suitable modification of the surrounding electromagnetic bath, as it can be achieved, e.g., with a cavity. The modified environment leads to a redistribution of the collective dressed state populations, such that squeezing is recovered at strong driving. In such modified environments, squeezing even occurs for a resonant driving field, in contrast to the regular vacuum case.

Coherent Phase Control of Multiphoton Ionization in Three-Level Ladder-Type System

We present the theoretical investigation of photoelectron spectroscopy resulting from the strong field induced multiphoton ionization in a typical three-level ladder-style system. Our theoretical results show that the photo-electron spectral structure can be alternatively steered by spectral phase modulation. This physical mechanism for strong field quantum control is explicitly exploited by the time-dependent dressed state population. It is concluded that the phase-shaped laser pulses can be used to selectively manipulate the multiphoton ionization process in complicated quantum systems.

Dressed states analysis of lasing without population inversion in a three-level ladder scheme: Approximate analytic time dependent solutions

A dressed-state study of lasing without population inversion from a three level atom interacting with a bi-chromatic laser field, in the ladder configuration, is formulated. We allow the atomic system to be dressed by both laser filed photons (double dressing). The evolution of the system under consideration is being explored both analytically and numerically, within the transient regime. Time dependent approximate analytic solutions for dressed-state populations and coherences are derived, within the so called “secular approximation,” under resonant conditions. We also present time dependent numerical solutions for population and coherences in the off-resonance regime. A spectral analysis is also performed revealing the structure of various dressed states transitions. These are shown to be composed of quintets centered about the frequencies of the coupling and probe laser fields and having sidebands located symmetrically at positions shifted from line center at the Rabi and double Rabi frequencies.

Dressed-state coherent population trapping in a V-type atom

We show theoretically that by applying a bichromatic electromagnetic field, the dressed states of a monochromatically driven two-level atom can be pumped into a coherent superposition termed dressed-state coherent population trapping. This effect can be viewed as a new key to manipulating a two-level system via its control over dressed-state populations. Applying this effect in the precision measurement of Rabi frequency, the unexpected population inversion and lasing without inversion is discussed to demonstrate such controllability.

Quantum control by selective population of dressed states using intense chirped femtosecond laser pulses

The physical mechanism of strong field quantum control using chirped femtosecond laser pulses is investigated. Dressed state control is exerted by making explicit use of the temporal phase changes of the pulse. In our experiment, the dressed state population is mapped by photoelectron spectra from simultaneous excitation and ionization of potassium atoms as a function of the chirp parameter. We show that chirped pulses can be used to selectively steer ground state atoms temporarily into a single dressed state realizing transient Selective Population of Dressed States (SPODS).

Quantum control by ultrafast dressed states tailoring

Strong field quantum control using shaped intense femtosecond laser pulses is investigated. The physical mechanism relies on selective population of dressed states (SPODS). With time resolved photoelectron spectroscopy the ultrafast dressed state population dynamics during the ionization of potassium atoms is directly observed. High selectivity of the dressed state population and tunability of the dressed state energies is demonstrated experimentally. Wave packet simulations on a diatomic model molecule confirm that SPODS is also applicable to molecules. We conclude that SPODS with simple ultrashort optimal pulse shapes is suitable for robust laser control of chemical reactions.

Quantum control and quantum control landscapes using intense shaped femtosecond pulses

A hitherto not considered physical mechanism of quantum control with intense shaped femtosecond laser pulses is investigated. Phase modulated pulses are used to exert control on the strong-field ionization of potassium atoms. We use a sinusoidal phase modulation function to manipulate the intensity of the Autler–Townes (AT) components in the photoelectron spectrum. The effect of all sine parameters is studied systematically. In addition, controllability is investigated using parameterized pulse shapes to generate a two-dimensional quantum control landscape. Our results show that the selective population of dressed states is the underlying strong-field physical mechanism. Due to its robustness with respect to the laser parameters, the selective dressed state population is an important general control mechanism.