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Annals of Physics

Quantum Coherence of a Two-Level System Interacting with Phonons in a Strong Time-Dependent Electric Field

Yuri I. Dakhnovskii

Published Feb 1, 1994• 45 citations
Publisher
DOI
10.1006/aphy.1994.1021

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Abstract Intervalence transitions between light and heavy mass subbands due to strong time‐varying electric fields are analyzed within the effective mass framework in two limiting cases, when the spin‐orbit interaction is weak and strong. Explicit formulae for the resonance lineshape, lineshift, and frequency of quantum mechanical Rabi oscillations are presented for one‐ and two‐photon absorption. The relationship between the detuning and the amplitude of Rabi oscillations is found to have exactly the same form, as in two‐level atomic systems. In case of p‐type germanium the Rabi oscillation period becomes comparable to the optical phonon scattering time at an intensity of the CO2‐laser of 5 MW/cm2. The conditions for the observation of Rabi oscillations are especially favourable at small energies of light quanta, when optical phonon emission due to energy conservation is forbidden. By this reason in p‐type semiconductors at strong time‐varying electric fields the non‐linear quantum effects similar to those found in two‐level atomic systems e.g. photon echos, self‐induced transparency etc., are expected to be observable as well.
Quantum two-level systems (TLSs) intrinsic to glasses induce decoherence in many modern quantum devices, such as superconducting qubits. Although the low-temperature physics of these TLSs is usually well-explained by a phenomenological standard tunneling model of independent TLSs, the nature of these TLSs, as well as their behavior out of equilibrium and at high energies above 1 K, remain inconclusive. Here we measure the non-equilibrium dielectric loss of TLSs in amorphous silicon using a superconducting resonator, where energies of TLSs are varied in time using a swept electric field. Our results show the existence of two distinct ensembles of TLSs, interacting weakly and strongly with phonons, where the latter also possesses anomalously large electric dipole moment. These results may shed new light on the low temperature characteristics of amorphous solids, and hold implications to experiments and applications in quantum devices using time-varying electric fields.