Non-Hermitian Magnon-Photon Interference in an Atomic Ensemble

Abstract

The beam-splitter (BS) is one of the most common and important components in modern optics, and lossless BS which features unitary transformation induces Hermitian evolution of light. However, the practical BS based on the conversion between different degree of freedoms are naturally non-Hermitian, as a result of essentially open quantum dynamics. In this work, we experimentally demonstrate a non-Hermitian BS for the interference between traveling photonic and localized magnonic modes. The non-Hermitian magnon-photon BS is achieved by the coherent and incoherent interaction mediated by the excited levels of atoms, which is reconfigurable by adjusting the detuning of excitation. Unconventional correlated interference pattern is observed at the photon and magnon output ports. Our work is potential for extending to single-quantum level to realize interference between a single photon and magnon, which provides an efficient and simple platform for future tests of non-Hermitian quantum physics.

Quantum Interference between Photons and Single Quanta of Stored Atomic Coherence

“…The phase sum θ + = θ 1 + θ 2 determines the nature of the quantum interference in the magnon-photon beamsplitter and is verified directly through the first-order interference of two distinct coherent states: an optical pulse with frequency ω sig and a spin wave stored via EIT [21], as shown in Fig. 2.…”

“…the exchange symmetry of the identical bosons at the beamsplitter, while antibunching stems from the Pauli exclusion principle that governs the quantum statistics of identical fermions [20]. However, if the beamsplitting operation is not unitary, as in the case of an open system with controllable dissipation, such as a cold atomic ensemble [21], the bosonic bunching statistics can be switched, with antibunching being also attainable [22][23][24]. The standard Hong-Ou-Mandel dip is thus reversed and, in stark contrast, a bump of enhanced coincidence is expected, therefore the probability of the state |1, 1 is not anymore negligible and can even dominate over all other possible outcomes.…”

“…The standard Hong-Ou-Mandel dip is thus reversed and, in stark contrast, a bump of enhanced coincidence is expected, therefore the probability of the state |1, 1 is not anymore negligible and can even dominate over all other possible outcomes. The recent realization of a non-Hermitian magnon-photon beamsplitting (MPBS) interface and the observation of controllable first-order interference between the light field and the stored spin wave [21] can lead to the first observation of this exotic behavior in a cold atomic ensemble.…”

“…For a thin atomic cloud, it is reasonable to assume that both the atomic spin wave as well as the photons are in a single mode, especially since we utilize the DLCZ scheme [25]. The transformation matrix that captures the essential features of their interactions is that of a MPBS [21,28], which can be in principle asymmetric and non-unitary, is [28][29][30],…”

Experimental Observation of Partial Parity-Time Symmetry and Its Phase Transition with a Laser-Driven Cesium Atomic Gas

“…In recent years, there have been intensive studies on the realization of optical PT symmetry in various physical settings, including waveguide and fiber arrays [11][12][13], photonic circuits and lattices [14,15], microtoroid resonators [16][17][18], trapped ions [19], etc. Compared to other materials, atomic media are desirable for realizing non-Hermitian Hamiltonians by synthesizing desired refractive index profiles due to their nice coherence property and the superiority for available active manipulations on light absorption, gain, dispersion, and nonlinearity, and so on [20][21][22][23][24][25][26][27].…”