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arXiv:1003.4100 · Physical Review A

Gains without inversion in quantum systems with broken parities

W. Z. Jia, L. F. Wei

Published Jul 12, 2010• 22 citations
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Abstract

For a quantum system with broken parity symmetry, selection rules cannot hold and cyclic transition structures are generated. With these loop transitions we discuss how to achieve inversionless gain of the probe field by properly setting the control and auxiliary fields. Possible implementations of our generic proposal with specific physical objects with broken parities (e.g., superconducting circuits and chiral molecules) are also discussed.

DOI
10.1103/physreva.82.013808

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For a quantum system with broken parity symmetry, selection rules cannot hold and cyclic transition structures are generated. With these loop transitions we discuss how to achieve inversionless gain of the probe field by properly setting the control and auxiliary fields. Possible implementations of our generic proposal with specific physical objects with broken parities (e.g., superconducting circuits and chiral molecules) are also discussed.
Abstract For quantum systems with broken parities, a transition can appear for any two different states, and cyclic transition structures can be generated for the lowest three levels. Based on these loop transitions, we discuss how to achieve high-precision localization effects for physical objects with broken parities, i.e . chiral molecules and asymmetric quantum wells. In a Δ-type three-level system interacting simultaneously with three external fields, one of which is a standing-wave field, the absorption spectrum carries information about the position of the objects. Moreover, we can achieve 100% probability of finding the objects at certain positions by choosing appropriate parameters. In addition, we present two possible implementations of the suggested scheme in a system comprising a mixture of left- and right-handed chiral molecules and asymmetric quantum wells and show how the phase-sensitive localization effect can be used to discriminate between enantiomeric molecules.
The concept of parity describes the inversion symmetry of a system and is of fundamental relevance in the standard model, quantum information processing, and field theory. In quantum electrodynamics, parity is conserved and large field gradients are required to engineer the parity of the light-matter interaction operator. In this work, we engineer a potassiumlike artificial atom represented by a specifically designed superconducting flux qubit. We control the wave function parity of the artificial atom with an effective orbital momentum provided by a resonator. By irradiating the artificial atom with spatially shaped microwave fields, we select the interaction parity in situ. In this way, we observe dipole and quadrupole selection rules for single state transitions and induce transparency via longitudinal coupling. Our work advances the design of tunable artificial multilevel atoms to a new level, which is particularly promising with respect to quantum chemistry simulations with near-term superconducting circuits.
Controlling the internal quantum states of chiral molecules for a selected enantiomer has a wide range of fundamental applications. Using tailored microwave fields, a chosen rotational state can be enriched for a selected enantiomer, even starting from a racemic mixture. This enables rapid switching between samples of different enantiomers in a given state, holding great promise, for instance, for measuring parity violation in chiral molecules. Achieving full enantiomer-specific state transfer is a key requirement for this and many other applications. Although theoretically feasible, achieving the required experimental conditions seemed unrealistic. Here, we realize near-ideal conditions, overcoming both the limitations of thermal population and spatial degeneracy in rotational states. Our results show that 96% state-specific enantiomeric purity can be obtained from a racemic mixture, in an approach that is universally applicable to all chiral molecules of C1 symmetry.
We show that quantum systems with broken symmetry can be selectively excited due to the coexistence of one- and two-photon transitions between the same states. Discrimination between two mirror-symmetric quantum wells or left- and right-handed chiral molecules can be accomplished by a ``cyclic population transfer'' process, in which one optically couples three system states $|1〉\ensuremath{\leftrightarrow}|2〉\ensuremath{\leftrightarrow}|3〉\ensuremath{\leftrightarrow}|1〉$, and completely transfers population from state ∣1〉|1〉∣1〉 to state ∣2〉|2〉∣2〉 and ∣3〉M|3{〉}_{M}∣3〉M​ (i.e., state ∣3〉|3〉∣3〉 of the mirror imaged system) or state ∣3〉|3〉∣3〉 and ∣2〉M|2{〉}_{M}∣2〉M​, depending on the laser phases.
We explore the possibility to generate new parity symmetry in the quantum Rabi model after a bias is introduced. In contrast to a mathematical treatment in a previous publication [J. Phys. A 46(2013) 265302], we consider a physically realistic method by involving an additional spin into the quantum Rabi model to couple with the original spin by an Ising interaction, and then the parity symmetry is broken as well as the scaling behavior of the ground state by introducing a bias. The rule can be found that the parity symmetry is broken by introducing a bias and then restored by adding new degrees of freedom. Experimental feasibility of realizing the models under discussion is investigated.