Fast Population Transfer Research Articles

Luminescence Properties of Closely Packed Organic Color Centers Grafted on a Carbon Nanotube.

We report on the photoluminescence of pairs of organic color centers in single-wall carbon nanotubes grafted with 3,5-dichlorobenzene. Using various techniques such as intensity correlations, superlocalization microscopy, and luminescence excitation spectroscopy, we distinguish two pairs of color centers grafted on the same nanotube; the distance between the pairs is on the order of several hundreds of nanometers. In contrast, by studying the strong temporal correlations in the spectral diffusion in the framework of the photoinduced Stark effect, we can estimate the distance within each pair to be on the order of a few nanometers. Finally, the electronic population dynamics is investigated using time-resolved luminescence and saturation measurements, showing a biexponential decay with a fast overall recombination (compatible with a fast population transfer between the color centers within a pair) and a weak delayed repopulation of the traps, possibly due to the diffusion of excitons along the tube axis.

Enantio-specific state transfer of chiral molecules through enantio-selective shortcut-to-adiabaticity paths.

An interesting method of fast enantio-specific state transfer (ESST) is proposed for cyclic three-level systems of chiral molecules. We show that the fast population transfer via shortcut to adiabaticity can be accomplished for the cyclic three-level system of a general (chiral) molecule with invariant-based inverse engineering of the coupling strengths. By choosing appropriate parameters, the two enantiomers, which are initially prepared in their ground states in the three-level systems, will evolve respectively along their enantio-selective shortcut-to-adiabaticity paths to different-energy final states simultaneously, thereby achieving the fast ESST.

Fast population transfer with a superconducting qutrit via non-Hermitian shortcut to adiabaticity

Non-Hermitian dissipation dynamics, capable of turning the conventionally detrimental decoherence effects to useful resources for state engineering, is highly attractive to quantum information processing. In this work, an effective scheme is developed for implementing fast population transfer with a superconducting qutrit via the non-Hermitian shortcut to adiabaticity (STA). We first deal with a Λ-configuration interaction between the qutrit and microwave drivings, in which the dephasing-assisted qubit state inversion requiring an overlarge dephasing rate is constructed non-adiabatically. After introducing a feasible ancillary driving that directly acts upon the qubit states, the target state transfer can be well realized but with an accessible qubit dephasing rate. Moreover, a high fidelity could be numerically obtained in the considered system. The strategy could provide a new route towards the non-Hermitian shortcut operations on superconducting quantum circuits.

Non-Hermitian shortcut to adiabaticity in Floquet cavity electromagnonics

Cavity magnon-polaritons have recently attracted intensive attention as a promising platform for exploring quantum phenomena. In this paper, we propose a Floquet engineering strategy to realize the non-Hermitian shortcut to adiabaticity in cavity magnon-polaritons. The nonadiabatic loss is restrained and the fast population transfer from the microwave photon to the magnon is realized. This model has potentially important applications in quantum information processing.

SU(3)-transformation-based inverse engineering for fast population transfer in three-level systems

We propose a scheme to inverse engineer the Hamiltonian of any general driven three-level system by employing a SU(3) transformation. For special cases, the scheme is then introduced to explore nonadiabatic dynamic evolution of systems with two-photon resonance. We demonstrate that, by selecting the control parameters with explicit function forms, both the ideal process and the practical evolution driving with the truncation of pulses, systematic error and decaying can implement fast population transfer with high fidelity. Moreover, the nonadiabatic passages are not reconstructed by the superadiabatic approach.

Construction of Rigorous Nonadiabatic Passages for Fast Population Transfer

Construction of Rigorous Nonadiabatic Passages for Fast Population Transfer

Stimulated Raman shortcut to adiabatic passage in chainwise and N-pod systems

The technique of stimulated Raman shortcut to adiabatic passage (STIRSAP) is implemented to chainwise and N-pod systems. In chainwise systems, for large detuning conditions, the population of the middle states can be suppressed during the time evolution of the system and therefore, the Hamiltonian of an N-state system is reduced to an effective two-level system, using adiabatic elimination technique. Applying the STIRSAP method in two-level systems, the modified Rabi frequencies for fast population transfer are achieved. For N + 1-pod systems, assuming that N Stokes pulses have the same time dependence, we reduce the Hamiltonian of the original system to a three-state system. For both resonance and detuning conditions, we can reduce the three-state Hamiltonian to an effective two-state one. Using the STIRSAP technique, robust population transfer can be achieved from an initial ground state to an arbitrary coherent superposition of all ground states.

Population transfer in a superconducting qutrit via shortcut to adiabaticity with optimized drivings

An efficient scheme is proposed for implementing fast population transfer in a superconducting qutrit via shortcut to adiabaticity (STA) with optimized drivings. An artificial atom of Cooper-pair box, having sufficient level anharmonicity, resonantly interacts with two classical microwave drivings. At two-photon resonance, the dynamical behavior of the qutrit can be described by a two-state system. By the technique of STA of counterdiabatic driving, the non-adiabatic coupling between two eigenstates can be nullified. Without increasing the number of applied drivings, we can implement the target state transfer only by modifying two original Gaussian-type pulses. Compared with the pulses required by the invariant-based operation, the modified pulses have the time profiles that are more accessible in experiment. With the available decoherence rates, high-fidelity population transfer can be obtained numerically. The strategy could offer a promising avenue towards optimized control over superconducting qutrits experimentally.

Efficient simulation of time- and frequency-resolved four-wave-mixing signals with a multiconfigurational Ehrenfest approach.

We have extended the multiconfigurational Ehrenfest approach to the simulation of four-wave-mixing signals of systems involving multiple electronic and vibrational degrees of freedom. As an illustration, we calculate signals of three widely used spectroscopic techniques, time- and frequency-resolved fluorescence spectroscopy, transient absorption spectroscopy, and two-dimensional (2D) electronic spectroscopy, for a two-electronic-state, twenty-four vibrational-mode conical intersection model. It has been shown that all these three spectroscopic signals characterize fast population transfer from the higher excited electronic state to the lower excited electronic state. While the time- and frequency-resolved spectrum maps the wave packet propagation exclusively on the electronically excited states, the transient absorption and 2D electronic spectra reflect the wave packet dynamics on both electronically excited states and the electronic ground state. Combining trajectory-guided Gaussian basis functions and the nonlinear response function formalism, the present approach provides a promising general technique for the applications of various Gaussian basis methods to the calculations of four-wave-mixing spectra of polyatomic molecules.

Fast population transfer and entanglement preparation among four superconducting flux qubits

We propose a scheme whereby we optimized the driven pulses applied on qubits to realize fast and robust population of quantum state transfer and entanglement generation between four superconducting flux qubits based on adiabatic passage. The quantum state was transferred from one qubit to another directly with high fidelity through applying an inverted set of pulses. Moreover, the resident time of the quantum state populated on the qubits could be controlled by adjusting the time delay between the driven pulses during the transfer process. Analysis of the dynamics demonstrates that the scheme is insensitive to inhomogeneous qubit–resonator coupling, and even for large detuning regimes of the qubit–resonator interaction, high-fidelity quantum state transfer and entanglement generation can be obtained. Our results also show that the effect of decoherence due to resonator decay and qubit relaxation could be negligible with currently existing technology.

Excited state dynamics of the s-trans-1, 3-butadiene cation: An ab initio quantum dynamical analysis

The excited state dynamics of the s-trans-1,3-butadiene cation, focusing on the second and third bands of the photoelectron spectrum, have been investigated using a fully quantal approach, for the first time. The five lowest electronic states X2Bg, A2Au, B2Ag, C2Bu, and D2Ag considering the six vibrational modes S3, S5, S13, S17, S19, and S20 were taken into account in the nuclear quantum dynamical investigation. The potential energy curves have been calculated along these coordinates for the five lowest electronic states using the RS2C method. Our simulations indicate a moderately fast population transfer from the A2Au and B2Ag to the X2Bg state, taking place on a time scale of 70-80 fs. Furthermore, the computed second and third bands of the photoelectron spectrum are in good agreement with the corresponding experimental ones. Our calculation identifies the symmetric stretching of the central C-C bond S5 and the symmetric C-C-C bending S13 to be the main progression modes of the second and third bands of the photoelectron spectrum of (cationic) s-trans-1,3-butadiene.

Fast quantum control in dissipative systems using dissipationless solutions

We report on a systematic geometric procedure, built up on solutions designed in the absence of dissipation, to mitigate the effects of dissipation in the control of open quantum systems. Our method addresses a standard class of open quantum systems that encompasses non-Hermitian Hamiltonians. It provides the analytical expression of the extra magnetic field to be superimposed to the driving field in order to compensate the geometric distortion induced by dissipation for spin systems, and produces an exact geometric optimization of fast population transfer. Interestingly, it also preserves the robustness properties of protocols originally optimized against noise. Its extension to two interacting spins restores a fidelity close to unity for the fast generation of Bell state in the presence of dissipation.

High Fidelity and Fast Population Transfer in a System of Interacting Two-Level Particles via Optimal Control

High fidelity population transfer is of fundamental importance in quantum information processing. This paper employs a multiple-constraint optimal control theory method to find optimal control fields for a quantum system of two two-level particles to implement fast population transfer with very high fidelity. Numerical simulations show that high fidelity and fast population transfer can be achieved by shaping ultrafast laser pulses in the framework of time domain. The dependence of fidelity on the time duration and the field amplitude of the laser pulses is also discussed.

Improving Shortcuts to Non-Hermitian Adiabaticity for Fast Population Transfer in Open Quantum Systems

It is still a challenge to experimentally realize shortcuts to adiabaticity (STA) for a non-Hermitian quantum system since a non-Hermitian quantum system's counterdiabatic driving Hamiltonian contains some unrealizable auxiliary control fields. In this paper, we relax the strict condition in constructing STA and propose a method to redesign a realizable supplementary Hamiltonian to construct non-Hermitian STA. The redesigned supplementary Hamiltonian can be eithersymmetric or asymmetric. For the sake of clearness, we apply this method to an Allen-Eberly model as an example to verify the validity of the optimized non-Hermitian STA. The numerical simulation demonstrates that a ultrafast population inversion could be realized in a two-level non-Hermitian system.

Effects of Charge Transfer State and Exciton Migration on Singlet Fission Dynamics in Organic Aggregates

A time-dependent wavepacket diffusion method is used to investigate the effects of charge transfer (CT) states, singlet exciton, and multiexciton migrations on singlet fission (SF) dynamics in organic aggregates. The results reveal that the incorporation of CT states can result in SF dynamics different from the direct interaction between singlet exciton and multiexciton, and an obvious SF interference is also observed between the direct channel and the indirect channel mediated by CT states. In the case of direct interaction, although the fast population transfer of singlet exciton in monomers, caused by the increase of exciton–exciton interaction, can accelerate the SF process, the spatial coherence alternatively has a counter-productive effect, and their competition leads to an optimal exciton–exciton interaction at which SF has a maximal rate. This trade-off relationship in SF dynamics is further analyzed from different perspectives, specifically in spatial and energy representations, and is also confi...

Controlling S2 Population in Cyanine Dyes Using Shaped Femtosecond Pulses.

Fast population transfer from higher to lower excited states occurs via internal conversion (IC) and is the basis of Kasha's rule, which states that spontaneous emission takes place from the lowest excited state of the same multiplicity. Photonic control over IC is of interest because it would allow direct influence over intramolecular nonradiative decay processes occurring in condensed phase. Here we tracked the S2 and S1 fluorescence yield for different cyanine dyes in solution as a function of linear chirp. For the cyanine dyes with polar solvation response IR144 and meso-piperidine substituted IR806, increased S2 emission was observed when using transform limited pulses, whereas chirped pulses led to increased S1 emission. The nonpolar solvated cyanine IR806, on the other hand, did not show S2 emission. A theoretical model, based on a nonperturbative solution of the equation of motion for the density matrix, is offered to explain and simulate the anomalous chirp dependence. Our findings, which depend on pulse properties beyond peak intensity, offer a photonic method to control S2 population thereby opening the door for the exploration of photochemical processes initiated from higher excited states.

Non-Hermitian shortcut to adiabaticity

A non-Hermitian shortcut to adiabaticity is introduced. By adding an imaginary term in the diagonal elements of the Hamiltonian of a two state quantum system, we show how one can cancel the nonadiabatic losses and perform an arbitrarily fast population transfer, without the need to increase the coupling. We apply this technique to two popular level-crossing models: the Landau-Zener model and the Allen-Eberly model.

Quantum-dynamical Modeling of the Rydberg to Valence Excited-State Internal Conversion in Cyclobutanone and Cyclopentanone

In this paper we present 4-state, 5-dimensional Vibronic Coupling Hamiltonians for cyclobutanone and cyclopentanone. Wave packet calculations using these Hamiltonians reveal that for cyclobutanone the (n,3s) to (n,π*) internal conversion involves direct motion in nuclear modes coupling the two states leading to fast population transfer. For cyclopentanone, internal vibrational energy redistribution is a bottleneck for activating reactive nuclear modes leading to slower population transfer.

Engineering of fast population transfer in three-level systems

We design, by invariant-based inverse engineering, resonant laser pulses to perform fast population transfers in three-level systems. The efficiency and laser intensities are examined for different protocols. The energy cost to improve the fidelity is quantified. The laser intensities can be reduced by populating the intermediate state and by multi-mode driving.

Symmetry, vibrational energy redistribution and vibronic coupling: The internal conversion processes of cycloketones

In this paper, we discern two basic mechanisms of internal conversion processes; one direct, where immediate activation of coupling modes leads to fast population transfer and one indirect, where internal vibrational energy redistribution leads to equidistribution of energy, i.e., ergodicity, and slower population transfer follows. Using model vibronic coupling Hamiltonians parameterized on the basis of coupled-cluster calculations, we investigate the nature of the Rydberg to valence excited-state internal conversion in two cycloketones, cyclobutanone and cyclopentanone. The two basic mechanisms can amply explain the significantly different time scales for this process in the two molecules, a difference which has also been reported in recent experimental findings [T. S. Kuhlman, T. I. Sølling, and K. B. Møller, ChemPhysChem. 13, 820 (2012)].