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Scientific Reports

A study of quantum Berezinskii–Kosterlitz–Thouless transition for parity-time symmetric quantum criticality

Sujit Sarkar

Published Mar 9, 2021• 9 citations
Publisher

Abstract

The Berezinskii-Kosterlitz-Thouless (BKT) mechanism governs the critical behavior of a wide range of many-body systems. We show here that this phenomenon is not restricted to conventional many body system but also for the strongly correlated parity-time (PT) symmetry quantum criticality. We show explicitly behaviour of topological excitation for the real and imaginary part of the potential are different through the analysis of second order and third order renormalization group (RG). One of the most interesting feature that we observe from our study the presence of hidden QBKT and also conventional QBKT for the real part of the potential whereas there is no such evidence for the imaginary part of the potential. We also present the exact solution for the RG flow lines. We show explicitly how the physics of single field double frequencies sine-Gordon Hamiltonian effectively transform to the dual field double frequencies sine-Gordon Hamiltonian for a certain regime of parameter space. This is the first example in any quantum many body systems. We present the results of second order and third order RG flow results explicitly for the real and imaginary part of the potential. This PT symmetric system can be experimentally tested in ultra-cold atoms. This work provides a new perspective for the PT symmetric quantum criticality.

DOI
10.1038/s41598-021-84485-2

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The Berezinskii-Kosterlitz-Thouless (BKT) mechanism governs the critical behavior of a wide range of many-body systems. We show here that this phenomenon is not restricted to conventional many body system but also for the strongly correlated parity-time (PT) symmetry quantum criticality. We show explicitly behaviour of topological excitation for the real and imaginary part of the potential are different through the analysis of second order and third order renormalization group (RG). One of the most interesting feature that we observe from our study the presence of hidden QBKT and also conventional QBKT for the real part of the potential whereas there is no such evidence for the imaginary part of the potential. We also present the exact solution for the RG flow lines. We show explicitly how the physics of single field double frequencies sine-Gordon Hamiltonian effectively transform to the dual field double frequencies sine-Gordon Hamiltonian for a certain regime of parameter space. This is the first example in any quantum many body systems. We present the results of second order and third order RG flow results explicitly for the real and imaginary part of the potential. This PT symmetric system can be experimentally tested in ultra-cold atoms. This work provides a new perspective for the PT symmetric quantum criticality.
We present extensive calculation and the results of quantum Berezinskii-Kosterlitz-Thouless (BKT) transition for interacting helical liquid system. This system shows the quantum BKT transition for the different physical situation which we present by two model Hamiltonians. We derive the renormalization group (RG) equations explicitly and present the flow lines behavior. We also present RG flow lines based on the exact solution. We observe that the Majorana fermion zero modes physics and the gapped Ising phase of the system. We also observe that the evidence of gapless Luttinger liquid phase as a common phase for both quantum BKT transitions.
An attempt is made to understand the quantum simulation of quantum Berezinskii–Kosterlitz–Thouless (QBKT) transition for interacting light-matter system. We derive the QBKT equation for our system along with the exact results. We present emergence of different quantum phases in the different regimes of parameter space for this quantum simulated system. We interpret the collective excitations of the system in terms of bosonic excitations (Bose metal phase) as well as the photon blocked state (photonic insulator state) in our study. We present the behavior of renormalization group (RG) flow lines from the numerical studies of RG flow equations and also from the exact solution. We study the quantum critical surface of the simulated model Hamiltonian and also present the exact results for Majumdar–Ghosh point as well as for refermionization point from the perspective of quantum simulation.
Abstract Emergence of different interesting and insightful phenomena at different length scale is the heart of quantum many-body system. We show that the physics of parity-time (PT) symmetry is one new addition to them. We show explicitly that the emergence of different topological excitation at different length scale for the PT symmetry system through the analysis of renormalization group (RG) flow lines. We observe that the higher order RG process favour the emergence of asymptotic freedom like behaviour and also show the effect of strong correlation on the emergent phases. Interestingly, the asymptotic freedom like behaviour is favoured by PT symmetry phase of the system. Moreover, we also derive the scaling relation for the couplings in RG equations. These findings can be tested experimentally in ultracold atoms.
The physics of the topological state of matter is the second revolution in quantum mechanics. We study the effect of interactions on the topological quantum phase transition and the quantum Berezinskii-Kosterlitz-Thouless (QBKT) transition in topological state of a quantum many-body condensed matter system. We predict a topological quantum phase transition from topological superconducting phase to an insulating phase for the interacting Kitaev chain. We observe interesting behaviour from the results of renormalization group study on the topological superconducting phase. We derive the renormalization group (RG) equation for QBKT through different routes with a few exact solutions along with the physical explanations, wherein we find the existence of two new important emergent phases apart from the two conventional phases of this model Hamiltonian. We also present results of a length-scale dependent study to predict asymptotic freedom like behaviour of the system. We do rigorous quantum field theoretical renormalization group calculations to solve this problem.
PT\mathcal{PT}PT-Symmetry Enhanced Berezinskii-Kosterlitz-Thouless Superfluidity
Berezinskii-Kosterlitz-Thouless (BKT) transition, the topological phase transition to a quasi-long range order in a two-dimensional (2D) system, is a hallmark of low-dimensional topological physics. The recent emergence of non-Hermitian physics, particularly parity-time (PT\mathcal{PT}PT) symmetry, raises a natural question about the fate of low-dimensional orders (e.g., BKT transition) in the presence of complex energy spectrum. Here we investigate the BKT phase transition in a 2D degenerate Fermi gas with an imaginary Zeeman field obeying PT\mathcal{PT}PT-symmetry. Despite complex energy spectrum, PT\mathcal{PT}PT-symmetry guarantees that the superfluid density and many other quantities are real. Surprisingly, the imaginary Zeeman field enhances the superfluid density, yielding higher BKT transition temperature than that in Hermitian systems. In the weak interaction region, the transition temperature can be much larger than that in the strong interaction limit. Our work showcases a surprising interplay between low-dimensional topological defects and non-Hermitian effects, paving the way for studying non-Hermitian low-dimensional phase transitions.
Synthetic non-conservative systems with parity-time (PT) symmetric gain-loss structures can exhibit unusual spontaneous symmetry breaking that accompanies spectral singularity. Recent studies on PT symmetry in optics and weakly interacting open quantum systems have revealed intriguing physical properties, yet many-body correlations still play no role. Here by extending the idea of PT symmetry to strongly correlated many-body systems, we report that a combination of spectral singularity and quantum criticality yields an exotic universality class which has no counterpart in known critical phenomena. Moreover, we find unconventional low-dimensional quantum criticality, where superfluid correlation is anomalously enhanced owing to non-monotonic renormalization group flows in a PT-symmetry-broken quantum critical phase, in stark contrast to the Berezinskii-Kosterlitz-Thouless paradigm. Our findings can be experimentally tested in ultracold atoms and predict critical phenomena beyond the Hermitian paradigm of quantum many-body physics.