Black holes permit matter to cross their event horizon in only one direction. We show that interacting bosons in optical lattices with asymmetric barrier exhibit an analogous phenomenon, creating unidirectional quantum transport without external driving or dissipation. This directionality emerges purely from many-body interactions, which cause asymmetric projection of the initial state onto transport-enabled or transport-forbidden sectors. The resulting dynamics create an effective one-way boundary in Hilbert space, forming a quantum analog of a black-hole event horizon. Our results establish interactions as a fundamentally new route to directional transport, enabling coherent rectification in atomtronic circuits by the use of intrinsic properties of the system only.
Black holes permit matter to cross their event horizon in only one direction. We show that interacting bosons in optical lattices with asymmetric barrier exhibit an analogous phenomenon, creating unidirectional quantum transport without external driving or dissipation. This directionality emerges purely from many-body interactions, which cause asymmetric projection of the initial state onto transport-enabled or transport-forbidden sectors. The resulting dynamics create an effective one-way boundary in Hilbert space, forming a quantum analog of a black-hole event horizon. Our results establish interactions as a fundamentally new route to directional transport, enabling coherent rectification in atomtronic circuits by the use of intrinsic properties of the system only.
The Hawking effect can be understood as a broad kinematic phenomenon associated with mode behavior near a horizon. While astrophysical black holes produce one specific realization of this radiation, this perspective inspires extensive theoretical and experimental efforts to create event horizons in diverse physical systems to observe the resulting analogue Hawking emission. One of the most successful realizations is the fiber-optical analogue, based on nonlinear quantum optics. In these notes, we introduce and motivate this system while outlining the theoretical concepts underlying the gravitational analogy. Finally, we review key experiments and discuss their impact on the field.
Quantum backflow, discovered quite a few years back, is a generic purely quantum phenomenon, in which the probability of finding a particle in a direction is nonzero (and increasing for a certain period of time) even when the particle has with certainty a velocity in the opposite direction. In this paper, we study quantum backflow of a quantum particle across the event horizon of a Schwarzschild black hole. In a toy model approach, we consider a superposition of two ingoing solutions and observe the probability density and probability current. We explicitly demonstrate a nonvanishing quantum back flow in a small region around the event horizon. This is in contrast to the classical black hole picture, that once an excitation crosses the horizon, it is lost forever from the outside world. Deeper implications of this phenomenon are speculated. We also study quantum backflow for another spacetime with horizon, the Rindler spacetime, where the phenomenon can be studied only within the Rindler wedge.
We show that reactive molecules with a unit probability of reaction naturally provide a simulator of some intriguing black hole physics. The unit reaction at the short distance acts as an event horizon and delivers a one-way traffic for matter waves passing through the potential barrier when two molecules interact by high partial-wave scatterings or dipole-dipole interactions. In particular, the scattering rate as a function of the incident energy exhibits a thermal-like distribution near the maximum of the interaction energy in the same manner as a scalar field scatters with the potential barrier outside the event horizon of a black hole. Such a thermal-like scattering can be extracted from the temperature-dependent two-body loss rate measured in experiments on KRb and other molecules.
This paper proposes that black holes can be described as globally coherent quantum systems, despite the emission of Hawking radiation. While the Hawking process induces a weak coupling between the interior and exterior regions, this interaction is demonstrated to be too small to produce significant decoherence for macroscopic and supermassive black holes. By treating the event horizon as a quasi-isolated, semi-transparent quantum interface, this framework reconciles semiclassical gravity with quantum unitarity. The black hole and its emitted radiation are modeled as a single, entangled pure quantum state that evolves unitarily. Key contributions of this work include: Formalization of the black hole-radiation system as a coherent quantum cavity. Mathematical derivation showing that the decoherence rate scales as Γ_dec ∝ M⁻⁸. Demonstration that for astrophysical black holes, the decoherence time τ_D is astronomically larger than the evaporation time t_evap, implying that global quantum coherence is effectively preserved. A potential resolution to the black hole information paradox within a unitary evolution framework. This research contributes to the ongoing theoretical discussion on the nature of event horizons, quantum information, and the holographic principle. Acknowledgements: I would like to express my deepest gratitude to my beloved dog, Milo, and my father, for their constant support, encouragement, and companionship throughout the development of this research.
In a recent paper [arXiv:2205.06279], Danielson et al. demonstrated that the mere presence of a black hole causes universal decoherence of quantum superpositions (dubbed the DSW decoherence). We analyze decoherence in a superconducting analogue [arXiv:1709.06154] of the event horizon of a black hole, where Andreev reflection plays the role of Hawking radiation. We consider a normal metal interferometer threaded by an Aharonov-Bohm flux, where one of the arms of the interferometer is coupled to a superconductor by a tunnel coupling of varying strength. At absolute zero temperature and for weak coupling, we find that the scattering states of the interferometer are decohered by Andreev reflection, a nontrivial manifestation of the proximity effect analogous to DSW decoherence from the event horizon of a black hole. However, for increasing coupling strength to the superconductor, we find a reemergence of coherence via resonant tunneling through Andreev bound states. This suggests the existence of an analogue gravitational phenomenon wherein transmission mediated by virtual Hawking radiation leads to a reemergence of coherence in an interferometer placed within a few Compton wavelengths of a black hole's event horizon.
Black holes are conventionally described as gravitational objects defined by spacetime geometry and event horizons. This geometric picture, while successful, leaves open fundamental questions concerning irreversibility, information isolation, and the universality of horizon-like behavior across physical systems. In this work, we propose and experimentally test an alternative framework: that horizon-like structures emerge as a consequence of realization dynamics, independent of gravity or spacetime curvature. By realization we mean the physical persistence of quantum structure under ongoing dynamics, as distinct from its mere mathematical existence in Hilbert space. Quantum structure that cannot be dynamically realized must be structurally excluded from the realizable domain. We implement a realization-based dynamical protocol on real superconducting quantum hardware provided by IBM Quantum, using sampler-native circuits without mid-circuit measurements or post-selection. A small quantum “world” subsystem is coupled to a non-realizable sink via a controllable realization barrier. Population of the sink qubit serves as an empirical signature of horizon-like absorption. Three regimes are experimentally compared: a fully realizable regime, a control regime with strong dynamics but no realization barrier, and a horizon regime in which unstable quantum structure is coherently redirected into the sink. Strong absorption is observed exclusively in the presence of the realization barrier, while the realizable and control regimes remain statistically indistinguishable. Control tests rule out noise, circuit depth, or strong driving as alternative explanations. These results constitute hardware-executed evidence that black-hole-like horizons can emerge purely from realization dynamics. We conclude that black holes may be understood as structural residues of completed realization rather than objects requiring gravitational collapse, opening a new experimental route to horizon physics grounded in quantum realization rather than geometry.