Observation of Critical Phenomena in Parity-Time-Symmetric Quantum Dynamics

Abstract

We experimentally simulate non-unitary quantum dynamics using a single-photon interferometric network and study the information flow between a parity-time (PT )-symmetric non-Hermitian system and its environment. We observe oscillations of quantum-state distinguishability and complete information retrieval in the PT -symmetry-unbroken regime. We then characterize in detail critical phenomena of the information flow near the exceptional point separating the PT -unbroken andbroken regimes, and demonstrate power-law behavior in key quantities such as the distinguishability and the recurrence time. We also reveal how the critical phenomena are affected by symmetry and initial conditions. Finally, introducing an ancilla as an environment and probing quantum entanglement between the system and the environment, we confirm that the observed information retrieval is induced by a finite-dimensional entanglement partner in the environment. Our work constitutes the first experimental characterization of critical phenomena in PT -symmetric non-unitary quantum dynamics.

High-order exceptional points in supersymmetric arrays

“…In the PT -symmetric phase, the eigenvalues are real and the intensities oscillate as a result of the nonorthogonality of eigenstates [17]; in the broken PTsymmetric phase, the intensities exponentially increase because of the complex eigenvalues [7]. Besides the coupled waveguide/resonator lattice, PT -symmetric systems are simulated by photonic quantum walks [18][19][20].…”

Quantum Sensing with a Single-Qubit Pseudo-Hermitian System

“…we adopt a Naimark dilation approach [20,22,52] using an extended Hermitian system. The evolution of the total system (including the system s and the ancilla qubit a) |Ψ(t) = |0 a ⊗ |ψ(t) s + |1 a ⊗ |χ(t) s follows a dilated Hamiltonian H [58].…”

“…Analysis of sensing performance.-The experimental realization of a pseudo-Hermitian qubit sensor relies on the conditional evolution in a dilated Hermitian quantum system [20,22,52]. This approach results in a finite success probability γ(λ o , τ ) (7.4 − 10.4 √ ε)ε 2 [58], which equals to the probability of the ancilla qubit in the state |0 a , see Fig.1.…”

“…ηH = H † η with a Hermitian invertible linear operator η) [6][7][8][9] can have real spectrum. The discovery has opened a new avenue to intriguing non-Hermitian physics in both classical and quantum systems [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24]. In particular, the concepts of exceptional point [25][26][27] and PT -phase transition [28,29] lead to important experimental observations such as single-mode lasers [30,31], non-reciprocal light transport [32,33], non-Hermitian topological light steering [34], asymmetric mode switching [35] and topological energy transfer [36] when encircling an exceptional point.…”

Experimental demonstration of one-sided device-independent self-testing of any pure two-qubit entangled state

“…2, our experimental setup consists of three modules: state preparation, Alice's measurement, and Bob's measurement. In the state preparation module, entangled photons are generated via type-I spontaneous parametric down-conversion (SPDC) [38][39][40][41][42][43][44][45][46][47][48]. By choosing the setting angle of the half-wave plate (HWP, H 0 ) to be cos 2χ = a, photon pairs are prepared into a family of entangled state |φ + = a |HH + √ 1 − a 2 |V V .…”