Dressed States Research Articles

Shortcut to adiabatic passage in a three-level system via a chosen path and its application in a complicated system.

We construct a shortcut to an adiabatic passage in a three-level system by choosing a dressed state acting as an evolutive path. Two designed auxiliary pulses are added into the original pulses to eliminate the couplings between the chosen evolutive-path state and the other two dressed states. The same target state as one gotten by adiabatic passage can be rapidly obtained, and the population of the lossy intermediate state can be controlled by setting proper parameters. Furthermore, as an example, we use this method in the adiabatic-passage scheme [Opt. Express20, 014547 (2012)], a complicated cavity quantum electrodynamics system, to successfully accelerate the generation of the three-dimensional entanglement between a single atom and a Bose-Einstein condensate.

Quantum dynamics of trapped ions in a dynamic field gradient using dressed states

Novel ion traps that provide either a static or a dynamic magnetic gradient field allow for the use of radio-frequency radiation for coupling internal and motional states of ions, which is essential for conditional quantum logic. We show that the Hamiltonian describing this coupling in the presence of a resonant dynamic gradient, is identical, in a dressed state basis, to the Hamiltonian in the case of a static gradient. The coupling strength is in both cases described by the same effective Lamb-Dicke parameter. This insight can be used to overcome demanding experimental requirements when using a dynamic gradient field for state-of-the-art experiments with trapped ions, for example, in quantum information science. At the same time, this insight opens new experimental perspectives by way of using a single resonant or detuned dynamic gradient field, inducing long-range coupling, for conditional multi-qubit dynamics.

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.

Ultrafast Control of the Polarity of BiCoO3 by Orbital Excitation as Investigated by Femtosecond Spectroscopy

In a polar material, a laser pulse can trigger nonlinear optical phenomena, such as second-harmonic generation (SHG). The authors investigate the variation of SHG in BiCoO${}_{3}$ upon irradiation with femtosecond terahertz pulses. Applying a THz pulse, they observe enhancement of SHG by more than 50% at room temperature, the response being so fast that it simply follows the THz pulse. This huge, ultrafast enhancement, explained in terms of a photon dressed state, could be used to control nonlinear optical properties at the femtosecond timescale.

Dressed Atom Fields and Dressed States in Waveguide Quantum Electrodynamics

The fully quantized problem of a dipole atom coupled to transverse electric fields is solved for both simple harmonic and two-level atoms in a general lossless electromagnetic environment. The method employed is a direct factorization of the Hamiltonian in terms of coupled excitations of atom and fields. Time evolution of the system is considered with emphasis on the effect of an atom-photon bound state. The rectangular waveguide is used as an example to illustrate the predicted behavior.

Subcycle Optical Response Caused by a Terahertz Dressed State with Phase-Locked Wave Functions.

The coherent interaction of light with matter imprints the phase information of the light field on the wave function of the photon-dressed electronic state. A driving electric field, together with a stable phase that is associated with the optical probe pulses, enables the role of the dressed state in the optical response to be investigated. We observed optical absorption strengths modulated on a subcycle time scale in a GaAs quantum well in the presence of a multicycle terahertz driving pulse using a near-infrared probe pulse. The measurements were in good agreement with the analytical formula that accounts for the optical susceptibilities caused by the dressed state of the excitons, which indicates that the output probe intensity was coherently reshaped by the excitonic sideband emissions.

Quarkonium Contribution to Meson Molecules

Starting from a molecular picture for the X(3872) resonance, this state and its J^{PC}=2++ HQSS partner [X2(4012)] are analyzed within a model which incorporates possible mixings with 2P charmonium states. Since it is reasonable to expect the bare chi_{c1}(2P) to be located above the D\bar D* threshold, but relatively close to it, the presence of the charmonium state provides an effective attraction that will contribute to bind the X(3872), but it will not appear in the 2++ sector. Indeed in this latter sector, the chi_{c2}(2P) should provide an effective small repulsion, because it is placed well below the D*\bar D* threshold. We show how the 1++ and 2++ bare charmonium poles are modified due to the D(*)\bar D(*) loop effects, and the first one is moved to the complex plane. The meson loops produce, besides some shifts in the masses of the charmonia, a finite width for the 1++ dressed charmonium state. On the other hand, the X(3872) and X2(4012) start developing some charmonium content, which is estimated by means of the compositeness Weinberg sum-rule. We also show that for X(3872) molecular probabilities of around 70-90 %, the X2 resonance destabilizes and disappears from the spectrum, becoming either a virtual state or being located deep into the complex plane, with decreasing influence in the D* \bar D* scattering line.

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.

Simulating Spatial Microwave Manipulation of Polyatomic Asymmetric-Top Molecules Using a Multi-Level Approach.

A numerical approach that employs a multi-level dressed state method to determine the AC-Stark shifts of molecular rotational energy levels is described. This approach goes beyond the two-level approximation often employed for simpler molecules, such as ammonia and acetonitrile, and is applicable to a variety of molecules. The calculations are used to develop experiments aimed at focusing, guiding, decelerating and trapping neutral, polyatomic, asymmetric-top molecules by using microwave fields. Herein, numerical calculations are performed for acetonitrile and 4-aminobenzonitrile. Based on these results, trajectory simulations are performed to predict the outcome of microwave focusing experiments in the TE1,1,p mode of a cylindrically symmetric microwave resonator. Simulations show that, for such an experimental setup, microwave focusing and guiding of 4-aminobenzonitrile requires starting longitudinal velocities close to, or below, 100 m s-1 , that is, much lower than values obtained with standard molecular beam techniques, such as supersonic expansion. Therefore, alternative beam-generation techniques, for example, buffer-gas-cooled molecular beams, are required to extend microwave manipulation methods to larger and more complex molecules.

Correlation functions in resonance fluorescence with spectral resolution: Signal-processing approach

In the framework of the signal processing approach to single-atom resonance fluorescence with spectral resolution, we diagrammatically derive an analytical formula for arbitrary-order spectral correlation functions of the scattered fields that pass through Fabry-Perot interferometers. Our general expression is then applied to study correlation signals in the limit of well separated spectral lines of the resonance fluorescence spectrum. In particular, we study the normalized second-order temporal intensity correlation functions in the case of the interferometers tuned to the components of the spectrum and obtain interferential corrections to the approximate results derived in the secular limit. In addition, we explore purely spectral correlations and show that they can fully be understood in terms of the two-photon cascades down the dressed state ladder.

Harmonic spectral modulation of an optical frequency comb to control the ultracold molecules formation

A method for creation of ultracold molecules by stepwise adiabatic passage from the Feshbach state to the fundamentally ground state using an optical frequency comb is presented within a semiclassical multilevel model. The sine modulation of the spectral phase of the comb leads to the creation of a quasi-dark dressed state. An insignificant population of the excited state manifold in this dark state provides an efficient way of mitigating decoherence in the system. In contrast, the cosine modulation does not lead to the quasi-dark state formation. The results demonstrate the importance of the parity of the spectral chirp in quantum control.

Dressing control of three-mode entanglement in two cascaded four-wave mixing

We report the control of the dressed state in three-mode optical entanglement in an N-type four-level system using two cascaded parametric amplification four-wave mixing steps inside an atom-like optical cavity and injected by thermal optical fields: a coherent field and the Einstein–Podolsky–Rosen field. First, cavity dressing results in Aulter–Towns-like (AT-like peak) anti-squeezing. And the three-cavity dressing interaction induces multi-AT-like peaks. Meanwhile, the cavity enhanced nonlinear gain results in one squeezing dip polariton. In addition, the coupling of three enhanced nonlinear gains brings about multi-dip squeezing. Second, as two nonlinear coefficients change, the nonlinear phase makes the squeezing profile (in phase, amplification) turn into an anti-squeezing profile due to nonlinear loss (out of phase, de-amplification). Finally, the squeezing profile can also be modified by field dressing (AT splitting, enhancement and suppression), and the squeezing degree is affected by injection fields. Thus, by judging the squeezing of three nonseparability criteria, we get three-mode optical entanglement.

Intensity–intensity and intensity–amplitude correlation of microwave photons from a superconducting artificial atom

We investigate the dynamics of the microwave-frequency nonclassical correlations in a three-level -configuration artificial atom, which is realized by superconducting quantum circuits. The intensity–intensity correlation and intensity field are strongly dependent on the relative phase of the driven fields. It is found that two interference loops are formed in the dressed state picture at or π, which are responsible for the generation of nonclassical microwave photons. When the phase is changed into or , the temporal correlation functions exhibit different oscillating behaviors. The phase-sensitive nonclassical correlations of fluorescence photons may find practical application in the design of all-optical switches and quantum information processing.

Molecular vibrational trapping revisited: a case study with D2.

The present theoretical study is concerned with the vibrational trapping or bond hardening, which is a well-known phenomenon predicted by a dressed state representation of small molecules like and in an intense laser field. This phenomenon is associated with a condition where the energy of the light induced, vibrational level coincides with one of the vibrational levels on the field-free potential curve, which at the same time maximizes the wave function overlap between these two levels. One-dimensional numerical simulations were performed to investigate this phenomenon in a more quantitative way than has been done previously by calculating the photodissociation probability of for a wide range of photon energy. The obtained results undoubtedly show that the nodal structure of the field-free vibrational wave functions plays a decisive role in the vibrational trapping, in addition to the current understanding of this phenomenon.

Steady-state entanglement of harmonic oscillators via dissipation in a single superconducting artificial atom

The correlated emission lasing (CEL) is experimentally demonstrated in harmonic oscillators coupled via a single three-level artificial atom [Phys. Rev. Lett. 115, 223603 (2015)] in which two-mode entanglement only exists in a certain time period when the harmonic oscillators are resonant with the atomic transitions. Here we examine this system and show that it is possible to obtain the steady-state entanglement when the two harmonic oscillators are resonant with Rabi sidebands. Applying dressed atomic states and Bogoliubov-mode transformation, we obtain the analytical results of the variance sum of a pair of Einstein-Podolsky-Rosen (EPR)-like operators. The stable entanglement originates from the dissipation process of the Bogoliubov modes because the atomic system can act as a reservoir in dressed state representation. We also show that the entanglement is robust against the dephasing rates of the superconducing atom, which is expected to have important applications in quantum information processing.

Speeding up Adiabatic Quantum State Transfer by Using Dressed States.

We develop new pulse schemes to significantly speed up adiabatic state transfer protocols. Our general strategy involves adding corrections to an initial control Hamiltonian that harness nonadiabatic transitions. These corrections define a set of dressed states that the system follows exactly during the state transfer. We apply this approach to stimulated Raman adiabatic passage protocols and show that a suitable choice of dressed states allows one to design fast protocols that do not require additional couplings, while simultaneously minimizing the occupancy of the "intermediate" level.

Triple-mode squeezing with dressed six-wave mixing

The theory of proof-of-principle triple-mode squeezing is proposed via spontaneous parametric six-wave mixing process in an atomic-cavity coupled system. Special attention is focused on the role of dressed state and nonlinear gain on triple-mode squeezing process. Using the dressed state theory, we find that optical squeezing and Autler-Towns splitting of cavity mode can be realized with nonlinear gain, while the efficiency and the location of maximum squeezing point can be effectively shaped by dressed state in atomic ensemble. Our proposal can find applications in multi-channel communication and multi-channel quantum imaging.

Two-dimensional infrared spectroscopy of vibrational polaritons of molecules in an optical cavity

Strong coupling of molecular vibrations to an infrared cavity mode affects their nature by creating dressed polariton states. We show how the single and double vibrational polariton manifolds may be controlled by varying the cavity coupling strength and probed by a time domain two-dimensional infrared (2DIR) technique, double quantum coherence. Applications are made to the amide-I (CO) and amide-II (CN) bond vibrations of N-methylacetamide.

Anticoherence in cavity QED systems: Influence from the associated baths beyond a Born approximation

The influence of the associated bath beyond a Born approximation (BA) is studied in a basic cavity QED system, i.e., the Rabi model coupled to a bath. It is shown that the application of a BA is valid only at zero temperature for all the baths, including the vacuum field and phonon bath associated with the two-state system, as well as the dissipative bath associated with the monochromatic optical mode. The non-BA process brings a different type of influence which stems from the inherent coupling between the quantum system and the associated bath and is against the building up of the dressed state. The physics behind this type of influence, which we term anticoherence, is analyzed, and a complete picture of influence from the associated bath is developed. To find the observed spectrum beyond a BA, we use the small-polaron theory to examine the state evolution under Fermi's golden rule, and based on it, the contribution from both the BA and non-BA processes can be calculated. The obtained result can help one to understand some peculiar observations in the strong-coupling regime.

Optimal efficiency of quantum transport in a disordered trimer.

Disordered quantum networks, such as those describing light-harvesting complexes, are often characterized by the presence of peripheral ringlike structures, where the excitation is initialized, and inner structures and reaction centers (RCs), where the excitation is trapped and transferred. The peripheral rings often display distinguished coherent features: Their eigenstates can be separated, with respect to the transfer of excitation, into two classes of superradiant and subradiant states. Both are important to optimize transfer efficiency. In the absence of disorder, superradiant states have an enhanced coupling strength to the RC, while the subradiant ones are basically decoupled from it. Static on-site disorder induces a coupling between subradiant and superradiant states, thus creating an indirect coupling to the RC. The problem of finding the optimal transfer conditions, as a function of both the RC energy and the disorder strength, is very complex even in the simplest network, namely, a three-level system. In this paper we analyze such trimeric structure, choosing as the initial condition an excitation on a subradiant state, rather than the more common choice of an excitation localized on a single site. We show that, while the optimal disorder is of the order of the superradiant coupling, the optimal detuning between the initial state and the RC energy strongly depends on system parameters: When the superradiant coupling is much larger than the energy gap between the superradiant and the subradiant levels, optimal transfer occurs if the RC energy is at resonance with the subradiant initial state, whereas we find an optimal RC energy at resonance with a virtual dressed state when the superradiant coupling is smaller than or comparable to the gap. The presence of dynamical noise, which induces dephasing and decoherence, affects the resonance structure of energy transfer producing an additional incoherent resonance peak, which corresponds to the RC energy being equal to the energy of the superradiant state.