Population Inversion In Two-level System Research Articles

High-fidelity population inversion of two-level system

Population inversion from an initial quantum state to a desired quantum state represents an exciting new frontier for quantum manipulation; that frontier is endowed with a strong interdisciplinary character and connections to other scientific fields, including atomic, molecular, and optical physics, as well as in solid-state devices, for fundamental studies, nuclear magnetic resonance and other spectroscopic techniques, metrology, interferometry, optical control of chemical reactions or quantum-information applications. Two-level systems are ubiquitous in these areas, and the driving of a population inversion is an important operation. So far various schemes for population transfer to a target state from an initial state have been proposed in theory and implemented in experiment. To be useful, such methods must, of course, be reliable, fast, and robust. Most literatures on two-level models investigated population inversion, which could be modelled by infinite-time processes. In this paper, by using a composite adiabatic passage (CAP) technique—in which the single pulse driving the quantum transition is replaced by a sequence of pulses with well-defined control phases, we investigate the population inversion problem of two-level quantum system with a finite duration. We take a sinusoidally varying pulse model that continuously vanishes at the beginning and the end of the finite duration as an example. The high-fidelity population inversion of the two-level system with finite duration is achieved. We discuss the effects of both coupling strength and detuning strength on the transition probability. It is found that this protocol could suppress the oscillations in the transition probability and reduce the admissible error bellow the 10 -4 quantum computation benchmark. The fidelity can arrive at 1, even with simple three- and five-composite pulse sequences. The protocol combines the advantages of adiabatic passage and composite pulses techniques. By choosing the composite phases appropriately, a high-fidelity, fast, stable and extremely robust complete population inversion is achieved for the finite-time two-level model. The values of the composite phases are universal for they do not depend on the pulse shapes and the chirp as long as the latter satisfy the symmetry property. Furthermore, the classical Hamiltonian is applied to describe the dynamic properties of the quantum system and further verify the effectiveness and feasibility of the proposed CAP technique. The results we present here are general and in principle apply to any two- and multi-level quantum systems. The accuracy of the CAP technique and its robustness against parameter variations make the protocol suitable for ultrahigh-fidelity quantum manipulation. We believe that the protocol can be widely used in many different areas of science, ranging from the quantum information, the quantum chemical, and the quantum optics to the ultracold atomic and molecular physics.

Population inversion in two-level systems possessing permanent dipoles

Bare-state population inversion is demonstrated in a two-level system with all dipole matrix elements nonzero. A laser field is resonantly driving the sample, whereas a second weaker and lower frequency coherent field additionally pumps it near resonance with the dynamically Stark-splitted states. Due to the existence of differing permanent dipole moments in the excited and ground bare states, quantum coherences among the involved dressed states are induced, leading to inversion in the steady state. Furthermore, large refractive indices are feasible, as well as the determination of the diagonal matrix elements via the absorption or emission spectra. The results apply to available biomolecular, spin, or asymmetric quantum dot systems.

All-optical modulation and amplification resulting from population inversion in two-level systems using a photonic-crystal cavity

I theoretically demonstrate all-optical modulation and amplification in a one-dimensional photonic-crystal (PC) cavity with a large number of two-level quantum dots (QD's). Populations in the ground and excited states of two-level QD's with large transition dipole moments are greatly changed by an external laser, and this affects the electrical susceptibility of the QD's. In other words, all-optical modulation, in which light (the signal light) is modulated by light (the external laser), becomes possible. Moreover, a large contrast of the electromagnetic local densities of states in the PC cavity enables steady-state population inversion in two-level systems, which is generally considered impossible. The output signal power is more than twice as large as the input power at certain frequencies.

Optical gain in NaI(T1) single crystals irradiated with intense photon pulses

The work reported here is a continuation of studies [i, 2] initiated by the assumption of the distinctive features of prompt charged particles in condensed media [3, 4]. On the basis of data from experimental studies of the processes that accompany the formation of prompt charged particles in condensed media we hypothesized [i] that in the end these processes result in the formation of spatially smeared high-intensity pulsed excitation sources in a much shorter time than for any relaxation processes removing excitation in the medium. The formation of such excitation sources in media characterized by, e.g., band structure anomalies causes population inversion in two-level systems with subsequent stimulated radiative recombination of excitation centers~ The conclusion that suggests itself is that there are evidently condensed media which can effectively manifest lasing properties under certain physical conditions and levels of nuclear radiation.

Nonadiabatic population inversion by laser frequency switching

Abstract Efficient nonadiabatic population inversion in two-level systems is predicted by theory in the case where a pulsed laser driving field of width ∼10 GHz through the resonance line with a rise time ∼65 ps.