Topological Protection and Control of Quantum Markovianity

Abstract

Under the Born-Markov approximation, a qubit system, such as a two-level atom, is known to undergo a memoryless decay of quantum coherence or excitation when weakly coupled to a featureless environment. Recently, it has been shown that unavoidable disorder in the environment is responsible for non-Markovian effects and information backflow from the environment into the system owing to Anderson localization. This turns disorder into a resource for enhancing non-Markovianity in the system-environment dynamics, which could be of relevance in cavity quantum electrodynamics. Here we consider the decoherence dynamics of a qubit weakly coupled to a two-dimensional bath with a nontrivial topological phase, such as a two-level atom embedded in a two-dimensional coupled-cavity array with a synthetic gauge field realizing a quantum-Hall bath, and show that Markovianity is protected against moderate disorder owing to the robustness of chiral edge modes in the quantum-Hall bath. Interestingly, switching off the gauge field, i.e., flipping the bath into a topological trivial phase, allows one to re-introduce non-Markovian effects. Such a result indicates that changing the topological phase of a bath by a tunable synthetic gauge field can be harnessed to control non-Markovian effects and quantum information backflow in a qubit-environment system.

Chiral quantum optics in the bulk of photonic quantum Hall systems

“…In these systems, topological features are exploited to realize complete chiral quantum optical setups, coupling their topological chiral edge channels to localized quantum emitters (or qubits) [24][25][26]. In parallel to such intense experimental efforts, new innovative theoretical proposals are constantly made to exploit these devices for new technological applications [27][28][29][30][31][32][33][34][35].…”

“…In this article we study the light-matter interaction dynamics of two-level quantum emitters coupled to a 2D photonic lattice subject to an homogeneous perpendicular synthetic magnetic field and an in-plane homogeneous synthetic electric field. Differently from the existing chiral quantum optics literature [7,21,22,30,31,33,34], which mostly focuses on light propagating along edge modes, here we investigate new strategies based on light propagation through the bulk of a 2D photonic system via the photonic analog of the Hall current. In the last decade, related anomalous transport and Berry curvature effects in the bulk of photonic systems have been the subject of several theoretical [36][37][38] and experimental [39][40][41] works, but have never been proposed as the operating principle of photonic devices.…”

Read-out of Quasi-periodic Systems using Qubits

“…In addition to such system specific studies of qubits as probes, there have also been theoretical proposals for reaching ultimate limits of thermometry using dephasing dynamics of a qubit [69,70] and experimental implementation of such thermometry using photonpolarization qubits [71]. Another important feature of our article that has received attention previously is the idea to use non-Markovianity of the qubit dynamics as a read-out mechanism [19,22,72,73]. In particular the proposal to evidence a structural phase transition in a trapped-ion chain using the non-markovian dynamics of one of the ionic qubits [31] in the chain and the study [74] suggesting to probe a topological phase transitions in the Su-Schreiffer-Heeger model, by measuring the non-markovianity in the decoherence dynamics of a coupled qubit are similar in spirity to our results to use non-markovianity to probe the localization-delocalization transition in the AAH model.…”

Light-matter interactions in synthetic magnetic fields: Landau-photon polaritons

“…These systems not only offer the possibility to simulate magnetic fields of unprecedented strength, but also allow to explore novel physical phenomena and applications, which are not accessible with their electronic counterparts. In particular, the ability to interface photons and phonons with atoms or solid-state emitters gives rise to a whole range of intriguing questions about the nature of light-matter interactions in magnetic and other topologically non-trivial environments [8][9][10][11][12][13][14][15][16][17][18][19][20].…”

“…In this Letter we study light-matter interactions in a 2D photonic lattice with an engineered synthetic magnetic field. Several previous works have already addressed the coupling of two-level systems to the chiral edge modes [8,[13][14][15]17], which can be used, for example, to transport classical or quantum information in a robust and unidirectional way [13,15,17,21,22]. Here we are interested in emitters coupled to the bulk region of the photonic lattice, where the presence of magnetic fields has dramatic consequences on the dynamics of the light emission process.…”