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European Quantum Electronics Conference (EQEC)

Coherent population trapping in two electron three-level systems with aligned spins

J. Mompart, R. Corbalán, L. Roso

Published Jan 1, 2003• 2 citations
Publisher

Abstract

This work investigates the possibility of realizing coherent population trapping (CPT) in a two-electron three-level system with parallel spins. Making an analogy with solid-state physics, this study demonstrates that a V-type three-level system with two electrons can be described as a /spl Lambda/-type three-level system for one single hole. Cancellation of the probe field absorption is obtained when the hole is placed in the dark state. Alternatively, in terms of the two-electron V-type system, the CPT condition is realized when one electron is placed in the ground state and the other one in the bright combination of the excited states. In addition, when the electron-electron Coulomb repulsion is taken into account, it is shown that this technique offers the possibility of measuring, with subnatural resolution, some superposition-state matrix elements of the electron-electron correlation that due to their time dependent nature are inaccessible by standard measuring procedures.

DOI
10.1109/eqec.2003.1313902

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This work investigates the possibility of realizing coherent population trapping (CPT) in a two-electron three-level system with parallel spins. Making an analogy with solid-state physics, this study demonstrates that a V-type three-level system with two electrons can be described as a /spl Lambda/-type three-level system for one single hole. Cancellation of the probe field absorption is obtained when the hole is placed in the dark state. Alternatively, in terms of the two-electron V-type system, the CPT condition is realized when one electron is placed in the ground state and the other one in the bright combination of the excited states. In addition, when the electron-electron Coulomb repulsion is taken into account, it is shown that this technique offers the possibility of measuring, with subnatural resolution, some superposition-state matrix elements of the electron-electron correlation that due to their time dependent nature are inaccessible by standard measuring procedures.
The possibility of coherent population trapping in two electron states with aligned spins (orthosystem) is evidenced. From the analysis of a three-level atomic system containing two electrons, and driven by the two laser fields needed for coherent population trapping, a conceptually new kind of dark state appears. The properties of this trapping are physically interpreted in terms of a dark hole, instead of a dark two-electron state. This technique, among many other applications, offers the possibility of measuring, with subnatural resolution, some superposition-state matrix elements of the electron-electron correlation that due to their time dependent nature are inaccessible by standard measuring procedures.
We observe coherent population trapping (CPT) in a two-electron atom— 174 Yb—using the transition. CPT is not possible for such a transition according to one-electron theory because the magnetic sublevels form a V-type system, but in a two-electron atom like Yb, the interaction of the electrons transforms the level structure into a Λ -type system, which allows the formation of a dark state and hence the observation of CPT. Since the two levels involved are degenerate, we use a magnetic field to lift the degeneracy. The single fluorescence dip then splits into five dips—the central unshifted one corresponds to coherent population oscillation, while the outer four are due to CPT. The linewidth of the CPT resonance is about 300 kHz and is limited by the natural linewidth of the excited state, which is to be expected because the excited state is involved in the formation of the dark state.
Three-level systems exhibit quantum interference effects absent in two-level systems, making them important for quantum optics. Here, we study the coherent interaction of a Lambda-type three-level system with free electrons shaped by optical near fields. By treating the electron train as a quantum drive, we show that the interplay between electron modulation and the three-level system's transition pathways induces tunable interference patterns. This interaction effectively realizes electron-mediated coherent population trapping (CPT). We identify a regime that enables complete population transfer between the two lower states and the preparation of a high-coherence superposition, manifested as dark states. In particular, these driven-dissipative steady states are independent of the initial state. Our work proposes shaped free electrons as a platform for steady-state coherent control of three-level systems, enabling atomic-scale state engineering.
Coherent population trapping (CPT) in a three-level system in the Λ configuration interacting with two quantized fields is studied. It is shown that, in addition to the known trapping states of the field involving ordinary coherent states of each mode, SU(2) coherent states associated with the Schwinger realization are also field states that give rise to CPT for this system. In addition it is pointed out that superpositions of such states, and statistical mixtures of them, for different total photon numbers also give rise to CPT. The stability of the CPT states against decay of the cavity field modes is examined. CPT is preserved if the modes decay at the same rate. A possible method for generating statistical mixtures of the SU(2) coherent states is described.
Three-level systems exhibit quantum interference effects absent in two-level systems, making them important for quantum optics. Here, we study the coherent interaction of a Λ-type three-level system with free electrons shaped by optical near fields. By treating the electron train as a quantum drive, we show that the interplay between electron modulation and the three-level system's transition pathways induces tunable interference patterns. This interaction effectively realizes electron-mediated coherent population trapping. We identify a regime that enables complete population transfer between the two lower states and the preparation of a high-coherence superposition, manifested as dark states. In particular, these driven-dissipative steady states are independent of the initial state. Our Letter proposes shaped free electrons as a platform for steady-state coherent control of three-level systems, enabling atomic-scale state engineering.
The phenomenon of coherent population trapping (CPT) of an atom (or solid state "artificial atom"), and the associated effect of electromagnetically induced transparency (EIT), are clear demonstrations of quantum interference due to coherence in multilevel quantum systems. We report observation of CPT in a superconducting phase qubit by simultaneously driving two coherent transitions in a Lambda-type configuration, utilizing the three lowest lying levels of a local minimum of a phase qubit. We observe 60(+/-7)% suppression of the excited state population under conditions of CPT resonance. We present data and matching theoretical simulations showing the development of CPT in time. Finally, we used the observed time dependence of the excited state population to characterize quantum dephasing times of the system.