Parity-time-symmetric quantum critical phenomena

Abstract

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.

Theory of Non-Hermitian Fermionic Superfluidity with a Complex-Valued Interaction

“…Such theoretical predictions have been confirmed experimentally by using optical systems and ultracold atoms [22][23][24][25][26][27][28][29][30]. However, since most of the previous studies dealt with single-particle physics, exploration of many-body physics in NH systems is still in its infancy [3][4][5][6][31][32][33][34].…”

“…NH quantum systems arise when the system undergoes dissipation to an environment [37,38]. It has been revealed that non-Hermiticity drastically alters the properties of a number of quantum phenomena that have been established in the Hermitian physics, such as quantum phase transitions [1][2][3][4], quantum critical behavior [5][6][7], topological phases [8][9][10][11][12][13][14][15][16][17], and magnetism [18]. Such theoretical predictions have been confirmed experimentally by using optical systems and ultracold atoms [22][23][24][25][26][27][28][29][30].…”

Non-Hermitian fractional quantum Hall states

“…Here e x(y) denotes the unit vector for each direction, and the lattice constant is set to unity. When we focus on the short-time evolution, the last term describing the quantum-jump is negligible [61][62][63][64]. In this case, we can see that the timeevolution is described by…”

Efficient variational approach to dynamics of a spatially extended bosonic Kondo model

“…This can be done by generalizing the variational state to Gaussian density matrices. Another interesting direction is to extend our approach to Markovian open quantum systems subject to dissipation [56,[106][107][108] and measurements [109][110][111][112][113] by employing the variational principle appropriate for master-equation dynamics [114,115]. Generalizing the decoupling canonical transformation, our approach can also be applied to multiple impurities [116] coupled to bosonic environments.…”