The ability of preparing perfect Bell pairs with a practical scheme is of great relevance for quantum communication as well as distributed quantum computing. We propose a scheme which probabilistically, but universally and unambiguously produces the $|{\mathrm{\Phi }}_{+}⟩$ Bell pair from four copies of qubit pairs initially in the same unknown pure quantum state. The same scheme, extended to eight qubit pairs initially in the same, moderately mixed quantum state, unambiguously produces the $|{\mathrm{\Phi }}_{+}⟩$ Bell pair with quadratically suppressed noise. The core step of the proposed scheme consists of a pair of local two-qubit operations applied at each of the two distant locations, followed by a partial projective measurement and postselection at each party, with results communicated classically. While the scheme resembles standard entanglement distillation protocols, it achieves success within just three iterations, making it attractive for real-world applications.

We show that states obtained from deep random Clifford circuits doped with non-Clifford phase gates (including $T$ gates and $\sqrt{T}$ gates) can be disentangled completely, provided the number of non-Clifford gates is smaller or approximately equal to the number of qubits. This implies that Pauli expectation values of such states can be efficiently simulated classically, despite them exhibiting both extensive entanglement and extensive nonstabilizerness. We prove this result analytically using a quantum error correction formulation, demonstrate its applicability numerically, and discuss consequences for the disentanglability of states generated through Hamiltonian dynamics. We show that this result implies a novel representation of approximate state designs that can also facilitate their efficient generation, and we propose a novel quantum circuit compression scheme for Clifford circuits doped with non-Clifford phase gates.

A theory for ground-state modifications of matter embedded in a Fabry-Perot cavity and whose excitations are described as harmonic oscillators is presented. Based on Lifshitz’s theory for vacuum energy and employing a Lorentz model for the material permittivity, a nonperturbative macroscopic QED model that accounts for the infinite number of cavity modes with a continuum of their wave vectors was built. Differences from the commonly used single-mode Hopfield Hamiltonian are revealed. The nonresonant role of polaritons in the ground-state energy shift is also demonstrated, showing that the cavity effect is mainly caused by static screening occurring at very low frequencies. The theory allows for a straightforward incorporation of losses and temperature effects.

Electronic and crystal structures of $\mathrm{Ce}({\mathrm{Ru}}_{1-x}{\mathrm{Rh}}_x{)}_2{\mathrm{Al}}_{10}$ have been studied using x-ray emission spectroscopy, photoelectron spectroscopy (PES), and x-ray diffraction. No structural phase transition was observed up to $x=0.1$, while the x-ray absorption spectra showed a Ce valence transition between $x=0.03$ and 0.05, accompanied by an increase in $c\text{−}f$ hybridization strength, suggesting a Lifshitz transition. Angle-resolved PES conducted on the $x=0.1$ sample revealed stronger hybridization along the $b$ axis compared to the other axes. Direction-dependent hybridization introduces complexity in applying conventional phase diagrams. For the first time, we propose a direction-dependent phase diagram for $\mathrm{Ce}({\mathrm{Ru}}_{1-x}{\mathrm{Rh}}_x{)}_2{\mathrm{Al}}_{10}$, advancing beyond the traditional Doniach phase diagram.

Quantum Hall states are characterized by a topological invariant, the many-body Chern number, which determines their quantized Hall conductivity. This invariant also emerges in circular dichroic responses, namely, by applying a circular drive and comparing excitation rates for opposite orientations. This work explores the dichroic response of confined, isolated quantum Hall systems, where bulk and edge contributions cancel exactly: When the edge response is properly isolated, the circular dichroic signal becomes quantized, serving as a direct and elegant probe of the many-body Chern number encoded in the edge physics. We demonstrate that this quantized edge response is entirely captured by low-energy chiral edge modes, allowing for a universal description of this effect based on Wen’s edge theory. Its low-energy nature implies that the quantized edge response can be distinguished from the bulk response in the frequency domain. The edge response is also shown to be a sensitive diagnostic of geometric features. This opens the possibility of characterizing the shape of quantum Hall droplets through edge spectroscopic measurements, without requiring knowledge of the system’s boundary profile. We illustrate our findings using realistic models of integer and fractional Chern insulators, with different edge geometries, and propose detection schemes suitable for ultracold atoms.

We develop a theory of a dynamical Dzyaloshinskii-Moriya interaction (dDMI) in centrosymmetric crystals by generally considering the vibration of both cations and anions. It gives rise to an antisymmetric spin-lattice coupling, inducing magnon-phonon hybridized topological excitations. Moreover, we find that this dDMI naturally exhibits a magnetoelectric feature, leading to the presence of dynamic multiferroicity with finite toroidal moment distribution in the momentum space. By comparing toroidal moments with band skyrmion structure, we reveal the intrinsic connection between band topology and dynamic multiferroicity through the dDMI.

Chemical activity is central in active matter, where local fuel consumption can lead to self-propulsion and phase separation. However, phase separation can also originate from passive physical interactions. To understand the influence of chemical activity on phase separation, we study mixtures where solvent species interconvert while solutes segregate. We demonstrate that such reactions affect phase separation by altering the chemical potential balance and by introducing an osmotic pressure difference at interfaces. However, the system does not permit a pseudopressure balance, and bulk compositions depend on which phases are in contact. Consequently, phase coexistence is no longer transitive, which enables self-propulsion and more complex dynamics.

We introduce a new framework for quantum channel discrimination in an adversarial setting, where the tester plays against an adversary. We show that in asymmetric hypothesis testing, the optimal type-II error exponent is precisely characterized by a new notion of quantum channel divergence (termed the minimum output channel divergence). This serves as a direct analog of the quantum Stein’s lemma in this new framework, and complements previous studies on “best-case” channel discrimination, thereby providing a complete understanding of the ultimate limits of quantum channel discrimination. Notably, the optimal error exponent can be achieved by simple nonadaptive adversarial strategies, and despite the need for regularization it remains efficiently computable and satisfies the strong converse property in general. Furthermore, we show that entropy accumulation, a powerful tool in quantum cryptography, can be reframed as an adversarial channel discrimination problem, establishing a new connection between quantum information theory and quantum cryptography.

We investigate the non-Hermitian (NH) attractive Hubbard model with spin depairing, which is a spin-resolved asymmetric hopping that nonreciprocally operates spins in the opposite direction. We find that spin depairing stabilizes a superfluid state unique to the NH system. This phase is characterized not only by a finite order parameter, but also by the emergence of exceptional points (EPs) in the momentum space—a feature that starkly contrasts with previously discussed NH fermionic superfluidity, where EPs are absent within the superfluid state and emerge only at the onset of the superfluid breakdown. We uncover the rich mechanism underlying this “exceptional fermionic superfluidity” by analyzing the interplay between EPs and the effective density of states of the complex energy dispersion. Furthermore, we reveal that the exceptional superfluid state breaks down induced by strong spin depairing on the cubic lattice, while it remains robust on the square lattice.

Matrix-product unitaries (MPUs) are many-body unitary operators that, as a consequence of their tensor-network structure, preserve the entanglement area law in 1D systems. However, it is unknown how to implement an MPU as a quantum circuit since the individual tensors describing the MPU are not unitary. In this Letter, we show that a large class of MPUs can be implemented with a polynomial-depth quantum circuit. For an $N$-site MPU built from a repeated bulk tensor with open boundary, we explicitly construct a quantum circuit of polynomial depth $T=O(N^{\alpha })$ realizing the MPU, where the constant $\alpha$ depends only on the bulk and boundary tensor and not the system size $N$. We show that this class includes nontrivial unitaries that generate long-range entanglement and, in particular, contains a large class of unitaries constructed from representations of $C^{*}$-weak Hopf algebras. Furthermore, we also adapt our construction to nonuniform translationally varying MPUs and show that they can be implemented by a circuit of depth $O(N^{\beta }\mathrm{poly}D)$ where $\beta \le 1+{\log }_2\sqrt{D}/s_{\min }$, with $D$ being the bond dimension and $s_{\min }$ the smallest nonzero Schmidt value of the normalized Choi state corresponding to the MPU.

Signal loss threatens the security of quantum cryptography, especially in quantum position verification (QPV) protocols, where even small losses can compromise security. This Letter modifies traditional QPV to make high transmission loss between verifiers and the prover irrelevant for a class of protocols, including a practically interesting one based on BB84 states (${\mathrm{QPV}}_{\mathrm{BB}84}^f$). Using photon presence detection and a small time delay, as well as a commitment before proceeding, the protocol’s relevant loss rate is reduced to only that of the prover’s lab, and the modified protocol has essentially the same security guarantees as the original one. The adapted protocol $\mathsf{c}\text{−}{\mathrm{QPV}}_{\mathrm{BB}84}^f$ thus offers strong security guarantees and feasibility over longer distances. We also discuss the practical implementation of the protocol and parameter estimates.