Abstract
The interplay between measurement and quantum correlations in many-body systems can lead to novel types of collective phenomena which are not accessible in isolated systems. In this work, we merge the Zeno-paradigm of quantum measurement theory with the concept of polarons in condensed-matter physics. The resulting quantum-Zeno Fermi-polaron is a quasi-particle which emerges for lossy impurities interacting with a quantum-degenerate bath of fermions. For loss rates of the order of the impurity-fermion binding energy the quasi-particle is short lived. However, we show that in the strongly dissipative regime of large loss rates a long-lived polaron branch re-emerges. This quantum-Zeno Fermi-polaron originates from the nontrivial interplay between the Fermi-surface and the surface of the momentum region forbidden by the quantum Zeno projection. The situation we consider here is realized naturally for polaritonic impurities in charge-tuneable semiconductors and can be also implemented using dressed atomic states in ultracold gases.
Highlights
The effect of measurement on the time evolution of a system is one of the most puzzling aspects of quantum dynamics [1,2], making it drastically distinct from its classical counterpart
We consider a situation where a strong dissipation acts on a subspace of the Hilbert space of an interacting quantum system, with the following question in mind: How are the many-body states affected by the emergence of a dissipation-induced constraint for the Hilbert space as the quantum-Zeno limit is approached? We focus on the paradigm of mobile quantum impurity problems at the border between few- and many-body physics and extend it to the regime of gain and loss of impurity particles
Technical details are presented in the Appendices, where, in particular, we introduce a Keldysh diagrammatic approach to nonequilibrium Green’s functions
Summary
The effect of measurement on the time evolution of a system is one of the most puzzling aspects of quantum dynamics [1,2], making it drastically distinct from its classical counterpart. In addition to the fundamental interest in exploring the effect of strong measurement on quantum many-body systems in general, the recent experiments in charge-tunable monolayer semiconductors open a new frontier to study polarons in the presence of impurity loss and gain, as the corresponding rates can become comparable to the timescales of unitary dynamics [39]. This leads to qualitative modifications of the dispersion of the impurity-fermion bound states as well as of the scattering continuum This complex interplay underlying the formation of the quantum-Zeno Fermi polaron requires a loss profile that can single out a nontrivial region in momentum space. This can be achieved by mixing the impurity with an additional lossy degree of freedom of much smaller mass. Technical details are presented in the Appendices, where, in particular, we introduce a Keldysh diagrammatic approach to nonequilibrium Green’s functions
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