Collective Quantum Tunneling Observed in Ultracold Atoms

Scientists have experimentally observed collective quantum tunneling in a system of ultracold atoms, a phenomenon predicted theoretically but challenging to verify. This study reveals how a group of atoms can synchronously pass through an energy barrier, behaving as a single quantum entity. The finding is crucial for understanding quantum coherence in many-body systems and opens new avenues for the development of quantum technologies. Quantum tunneling is a cornerstone of quantum mechanics, where a particle can "pass through" an energy barrier that would classically be insurmountable. However, observing this effect collectively, where multiple particles act in concert, has been an experimental challenge. Previous research focused on individual particle tunneling or systems with weak collective interactions. This new work, in contrast, demonstrates strong correlation in the tunneling process of an atomic ensemble. To achieve this observation, the team used an optical trap to confine rubidium-87 atoms at temperatures near absolute zero, creating a Bose-Einstein condensate. Through precise manipulation of magnetic fields and lasers, they generated a potential barrier and observed how a coherent group of these atoms tunneled through it. The results showed that the probability and speed of tunneling depended on the interactions between the atoms, confirming the collective nature of the phenomenon. This breakthrough has significant implications for fundamental and applied physics. It allows for a deeper understanding of quantum coherence and the dynamics of complex quantum systems, which is essential for the design of quantum computers and high-precision sensors. Furthermore, it could inspire new research into collective quantum phenomena in exotic materials and biological systems, where tunneling plays an important role.

Coherent Control of Energy Transport at Room Temperature

A method has been proposed for coherently controlling energy transport in a reaction-center-connected donor-acceptor system, operating in a non-equilibrium steady-state (NESS) and at room temperature. This advancement suggests the possibility of manipulating energy flow using phase-controlled coherent fields, even in noisy and dissipative environments, extending the scope of quantum control techniques beyond traditionally studied transient and low-dissipation regimes. The model considers pigments continuously interacting with incoherent radiation and a phonon bath, while being driven by phase-controlled coherent fields. Coherent excitation of the donor-acceptor pair is shown to induce interference between excitation pathways, resulting in phase-dependent modulation of the flux. This interference allows for both enhancement and suppression of energy transfer, effectively acting as an optical energy switch. The persistence of this interference in a NESS under dissipative conditions is a key finding. Traditionally, coherent quantum control has been associated with low-dissipation conditions and transient states. Demonstrating its viability at room temperature and in noisy environments opens new avenues for designing devices that harness quantum phenomena under more realistic and accessible operating conditions, with potential applications in energy efficiency and photonics.

New Method for Excitation Spectra in Non-Uniform Quantum Systems

Researchers have developed a new tangent-space method to study the excitation spectra of non-uniform quantum many-body systems with open boundary conditions. The technique focuses on algebraic varieties of matrix product states (MPS), an efficient representation of quantum states that allows for the simulation of complex systems. This advance is crucial for understanding the dynamics of heterogeneous quantum systems, where properties vary spatially, a common scenario in quantum devices and advanced materials. 1The method introduces a "rank tomography" of the MPS tangent space, which quantifies the expressive power of these states in terms of the particle-sector rank profiles of the underlying MPS variety. This characterization allows for the evaluation of the fidelity with which MPS can describe system excitations, providing a tool to optimize simulations and understand their limitations. The ability to analyze expressivity is fundamental for the design and interpretation of experiments with many-body quantum systems. To validate the methodology, it was applied to the Bose-Hubbard model, a benchmark system in condensed matter physics that describes interacting bosons on a lattice. The results demonstrate that the method accurately reproduces low-lying excitations and, significantly, captures finite-size precursors of the Mott-insulator to superfluid transition. This ability to identify phase transitions in finite systems is an important step towards understanding emergent quantum phenomena in real materials and engineering new quantum devices.

Vector Dark Matter: Parametric Resonance Requires New Inflationary Conditions

A new study explores the viability of vector dark matter (VDM) production via parametric resonance in a Higgsed Abelian sector. This mechanism, which involves the amplification of a dark-Higgs field to generate VDM particles, critically depends on the initial displacement conditions of the dark-Higgs field. Researchers analyzed this problem using a calibrated nonlinear broad-resonance relic map and a stochastic inflationary analysis of the dark-Higgs condensate. The results show that a minimal light-spectator realization fails under standard inflationary duration. For broad resonance and isocurvature constraints to hold, an initial dark-Higgs field displacement of \( φ_0/H_I \gtrsim 3.3 imes10^4 \) is required, where \( H_I \) is the Hubble scale during inflation. However, stochastic equilibrium and finite-duration random walk only produce \( φ/H_I=\mathcal O(1) \). This large mismatch in initial displacement represents a robust, model-independent obstruction to the stochastic branch of VDM production. The study identifies a distinct, classically sourced branch where the condensate tracks a time-dependent minimum, \( φ_0=κH_*/\sqrt{λ_4} \), induced by a negative Hubble-induced mass. In this scenario, the radial fluctuation remains heavy during inflation. This sourced branch modifies the scaling relation of the dark matter particle mass, \( m_X \), from \( m_X\propto λ_4^{5/8}H_I^{-3/2} \) to \( m_X\propto κ^{-3/2}λ_4 H_*^{-3/2} \). The authors derived the simultaneous consistency conditions for this branch, including broad resonance, adiabatic tracking, perturbativity, sub-Planckian displacement, thermal non-erasure, spectator backreaction, and control of inflationary vector fluctuations. These findings suggest that Higgsed-vector resonance is not merely a dark matter production mechanism, but also a sensitive probe of the inflationary and reheating dynamics that determine its initial conditions. The work opens new avenues for exploring the connection between dark matter physics and early cosmological processes, potentially leading to tighter constraints on inflation models and the nature of dark matter.

Noisy Quantum Hardware Reveals Identifiable Fingerprints in Cloud Computing

Researchers have developed a formal framework for quantum hardware identifiability, revealing that outputs from cloud-based quantum computers contain "fingerprints" that can identify the underlying physical device. This finding has significant implications for privacy and security in quantum cloud computing, where providers often aim to conceal implementation details or the identity of the hardware used. The work introduces the concept of "routing anonymity" as a crucial security notion for these services. The study formalizes hardware identifiability as a hypothesis-testing problem and demonstrates that routing anonymity decays exponentially with passive access to a single backend. Furthermore, the researchers establish a fundamental utility-anonymity trade-off, which imposes limits on how much backend-specific information can be removed from classical outputs without degrading their usefulness. To validate their theory, the scientists conducted experiments on Amazon Braket, utilizing ion-trap and superconducting quantum processors. They observed 87-90% classification between different superconducting backends and 96-100% classification across physical platforms, even after applying natural forms of post-processing. These results confirm that identifying fingerprints are an inherent intermediate-depth phenomenon for noisy quantum hardware, establishing a "depth principle" using Pauli-transfer-matrix tools. Collectively, this research establishes routing anonymity as a distinct security requirement for quantum cloud computing and provides a framework for quantifying and controlling the utility-anonymity trade-off. This opens avenues for future investigations into how to protect both user and provider privacy in an evolving quantum ecosystem.