Time-correlated Stokes–anti-Stokes (SaS) scattering has been studied in different transparent media, more frequently in diamond. While the nonclassical nature of the SaS scattered photons has been well established, the presence of entanglement in this spontaneous four-wave mixing process has not been demonstrated. Here, we show the violation of the Bell-type Clauser-Horne-Shimony-Holt inequality for the polarization of SaS photon pairs near a Raman resonance in diamond. The degree of entanglement depends on the detuning of the photon pairs from the degenerate two-photon pump and on the orientation of the polarization of the incident light with respect to the crystallographic orientation of the sample. This result opens up the possibility to tailor the quantum state of photon pairs without stringent constraints of phase matching and to combine quantum optics and SaS Raman spectroscopy for new applications in materials science and quantum information.

We study the quantum fluctuation theorem in the one-time measurement (OTM) scheme, where the work distribution of the backward process has been lacking and which is considered to be more informative than the two-time measurement (TTM) scheme. We find that the OTM scheme is the quantum nondemolition TTM scheme, in which the final state is a pointer state of the second measurement whose Hamiltonian is conditioned on the first measurement outcome. Then, by clarifying the backward work distribution in the OTM scheme, we derive the detailed fluctuation theorem in the OTM scheme for the characteristic functions of the forward and backward work distributions, which captures the detailed information about the irreversibility and can be applied to quantum thermometry. We also verified our conceptual findings with the IBM quantum computer. Our result clarifies that the laws of thermodynamics at the nanoscale are dependent on the choice of the measurement and may provide experimentalists with a concrete strategy to explore laws of thermodynamics at the nanoscale by protecting quantum coherence and correlations.

We experimentally study the ability of a broadband “loop-and-switch” type quantum memory device to store entanglement. We find that one active loop-based memory and one passive fiber delay line can be used to faithfully store two polarization-entangled photons and demonstrate a rudimentary entanglement distribution protocol. The entangled photons are produced by a conventional spontaneous parametric down-conversion source with center wavelengths at 780 nm and bandwidths of $\sim 10$ THz, while the memory has an even wider operational bandwidth that is enabled by the weakly dispersive nature of the Pockels effect used for polarization-insensitive active switching. These results help demonstrate the utility of loop-based quantum memories for quantum networking applications.

We use the Gross-Pitaevskii equation (GPe) to study the motion of a heavy impurity immersed in a weakly interacting Bose-Einstein condensate and interacting with the bosons via an attractive boson-impurity potential. We construct a perturbative solution to the GPe in powers of impurity velocity in the case when the boson-impurity potential is tuned to unitarity, resulting in a unitary polaron, and calculate its effective mass. In addition, we calculate the interaction energy of two unitary polarons which are sufficiently far apart. Our formalism also reproduces the results for both the mass and interaction energy obtained at weak boson-impurity coupling.

We consider a system comprising two groups of quantum dimers placed in a common electromagnetic cavity and controlled by selectively applying a static external potential to one of the groups. We show that in the regime of deep strong coupling to vacuum electromagnetic fluctuations, the emergent photon-assisted interaction between the dimers, leads to a strongly nonlinear quantized cross-polarization response of the first, unbiased group of dimers to the potential applied to the second group. The total polarization shows a series of almost ideal steps whose number and position depends on the parity of the numbers of dimers in the groups. This nonperturbative effect is a distinctive feature of mesoscopic systems comprising a finite number of dimers and disappears in the thermodynamic limit which is commonly used in the description of the generalized Dicke models.

We investigate the contribution of negative-energy states on the $E2$ and $M1$ polarizabilities for the ${}^{1}S_0$ and ${}^{3}P_0$ states of the Sr clock and find that they dominate the $E2\text{−}M1$ polarizability difference. Our calculated result is $-7.74\left(3.92\right)\times {10}^{-5}$ a.u., which resolves the sign inconsistency between theory and experiment. Additionally, we extend our method to other optical clocks, confirming the crucial role of negative-energy states in determining the $M1$ polarizability.

We address the problem of lattice light shifts in the Sr clock caused by multipolar $M1$ and $E2$ atom-field interactions. We present a simple but accurate formula for the magnetic-dipole polarizability that takes into account the contributions of both the positive- and negative-energy states. We calculate the contribution of negative-energy states to the $M1$ polarizabilities of the clock ${}^1{S}_0$ and ${}^3{P}_0^o$ states at the magic frequency. Taking these contributions into account, we obtain good agreement with the experimental results, explaining the major discrepancy between theory and experiment.

We report an experimental investigation of conditional majorization uncertainty relations (CMURs) in the presence of quantum memory. We find that the CMUR bounds are always physically nontrivial even if the particle of interest is strongly entangled with a quantum memory, whereas the previous conditional entropic uncertainty relation bounds may be trivial and physically unreachable. We deploy vectorized measures of uncertainty relations and quantum correlations, and the result reveals the sophisticated structures of them. In addition, we demonstrate an application of the CMURs, to witness steerability of bipartite states. Such a method applies to an arbitrary number of measurement settings and can be efficiently implemented. Aside from the CMURs' fundamental significance, our result also shows its impact on the development of future quantum technologies.

Trapped ions provide a platform for quantum technologies that offers long coherence times and high degrees of scalability and controllability. Here, we use this platform to develop a realistic model of a thermal device consisting of two laser-driven, strongly coupled Rydberg ions in a harmonic trap. We show that the translational degrees of freedom of this system can be utilized as a flywheel storing the work output that is generated by a cyclic thermodynamic process applied to its electronic degrees of freedom. Mimicking such a process through periodic variations of external control parameters, we use a mean-field approach underpinned by numerical and analytical calculations to identify relevant physical processes and to determine the charging rate of the flywheel. Our work paves the way for the design of microscopic thermal machines based on Rydberg ions that can be equipped with both many-body working media and universal work storages.

The energy-time degree of freedom has emerged as a promising avenue for photonic quantum technologies due to its intrinsic robustness against decoherence; however, the timescales associated with energy-time entangled photons make for difficult measurement and manipulation. We implement two optical Kerr gates, in short (35 mm) pieces of single-mode fiber, to achieve ultrafast measurement of the time correlations of energy-time entangled photon pairs, with resolutions of $320\pm 30$ fs and $290\pm 30$ fs for signal and idler photons, respectively. These measurements, in addition to joint spectral measurements of the photon-pair state, are used to verify entanglement by means of the violation of a time-bandwidth inequality. Without the need for an interferometric setup or frequency conversion, the optical Kerr shutter is a valuable addition to the ultrafast quantum optics control and metrology toolbox.

Quantum steering is an asymmetric form of quantum nonlocality where one can trust the measurements of one of the parties. In this work, inspired by practical considerations, we investigate the scenario in which one cannot fully trust their measurement devices, just up to some level of precision. We first find the effect of such an imprecision on standard device-dependent quantum tomography. We then utilize this result to compute the variation in the local bound of any general steering inequality depending on the amount of trust one puts in one of the party's measurement devices. This is particularly important as we show that even a small distrust on Alice might cause the parties to observe steerability even if the quantum state is unsteerable. Furthermore, this effect becomes more relevant when observing higher-dimensional quantum steering.

We consider the origin of unpolarized light resulting from the backscattering of circularly polarized light by a random turbid tissuelike disperse medium. We reveal the dynamics of the backscattered fraction of unpolarized light, disclosing its meticulous decomposition into two rigorously polarized components characterized by opposing helicities, with fully defined polarization states. Concurrently, their superposition, driven by multiple scattering within the medium, leads to the appearance of a fraction of linear polarization. We emphasize that the in-depth binding of circular polarization memory of light when the helicity flips occurs within the scattering medium, meaning the conservation of spin angular momentum. We anticipate that the results obtained hold significant implications for future studies, particularly in the field of tissue polarimetry and light vortices.

We systematically test a quasiclassical spin model of a large spin lattice in energy space, with a tunable, reversible Hamiltonian and effective long-range interactions. The system is simulated by a weakly interacting Fermi gas undergoing perturbed quantum rewinding using rf pulses. With single-shot analysis techniques, the measurement of energy-resolved spin density quantitatively substantiates the classical treatment of this many-body spin system. This work also elucidates the effects of rf detunings on the system and measurements, pointing the way to new correlation measurement methods.

We explore the boundary time-crystal transition at the level of quantum trajectories which result from continuous monitoring. This Letter is motivated by recent experiments [G. Ferioli, A. Glicenstein, I. Ferrier-Barbut, and A. Browaeys, Nat. Phys. 19, 1345 (2023)] realizing this many-body system and which allow one in principle to gain in situ information on its nonequilibrium dynamics. We find that the photon count signal as well as the homodyne current allow one to identify and characterize critical behavior at the time-crystal phase transition. In the time-crystal phase these quantities display persistent oscillations, resolvable in finite systems and in individual realizations. At the transition point the dynamics of the emission signals feature intermittent strong fluctuations, which can be understood through a simple nonlinear phase model. We furthermore show that the time-integrated homodyne current can serve as a useful dynamical order parameter. From this perspective the time crystal can be viewed as a state of matter in which different oscillation patterns coexist.

We demonstrate that the equality-based first law of thermodynamics inherently implies a universal Landauer-like inequality, connecting variations in system entropy and energy. This Landauer-like inequality is shown to depend solely on system information and is highly applicable in scenarios where the implementation of the conventional Landauer principle becomes challenging. Moreover, we unveil that this Landauer-like inequality complements the Landauer principle by establishing an alternative upper bound on heat dissipation. To underscore its practicality, we illustrate the utility of the Landauer-like inequality in contexts such as dissipative quantum state preparation and quantum information erasure applications. Our findings offer insights into identifying thermodynamic constraints, with particular relevance to the domains of quantum thermodynamics and the energetics of quantum information processing. Additionally, this approach paves the way for investigating systems coupled to nonthermal baths or those characterized by limited access to bath information.

We study the field chirality at the exceptional points (EPs) in an optical whispering gallery mode (WGM) microcavity, which is commonly believed to be globally perfect. We have discovered a locally imperfect or locally perfect chirality of eigenmodes at the EPs in a WGM microcavity perturbed by two strong nanoscatterers. We find that the generally local and imperfect chirality at the EPs tends to be globally perfect with the decrease of the scattering effect induced by the nanoscatterers, and the chirality also becomes locally perfect with the decrease of the relative azimuthal angle between the two strong nanoscatterers. With a first-principles-based model considering a dynamic multiple-scattering process of the azimuthally propagating modes (APMs), all the above counterintuitive phenomena of imperfect or perfect chirality can be respectively explained by a strong or weak frequency dependence of the APM scattering coefficients at an effective scatterer composed of the two nanoscatterers. In this paper, we provide increased understanding of the general properties of chirality at EPs which will benefit potential applications enabled by the chirality features of non-Hermitian systems at EPs.

Quantum networks are of high interest nowadays. In short, they describe the distribution of quantum sources represented by edges to different parties represented by nodes in the networks. Bundles of tools have been developed recently to characterize quantum states from the network in the ideal case. However, features of quantum networks in the noisy intermediate-scale quantum (NISQ) era invalidate most of them and call for feasible tools. By utilizing purity, covariance, and topology of quantum networks, we provide a systematic approach to tackle with arbitrary quantum networks in the NISQ era, which can be noisy, intermediate-scale, random, and sparse. One application of our method is to witness the progress of essential elements in quantum networks, like the quality of multipartite entangled sources and quantum memory.

The quantum mechanical weak value $A_w=\langle \varphi \left|A\right|\psi \rangle /\langle \varphi |\psi \rangle$ of an observable $A$ is a measurable quantity associated with an observable $A$ and pre- and postselected states $|\psi \rangle ,|\varphi \rangle$. Much has been discussed about the meaning and metrological uses of anomalous weak values, lying outside of the range of eigenvalues of $A$. We present a simple proof that anomalous weak values require that the (possibly mixed) pre- and postselection states have coherence in the eigenbasis of $A$. We also present conditions under which anomalous $A_w$ are witnesses of generalized contextuality, dispensing with the operational weak measurement setup.

We report on the direct optical production and spectroscopy of ${}^1{S}_0\text{−}{}^3{P}_0$ molecules with large binding energy using the clock transition of ${}^{\text{171}}\text{Yb}$, and on the observation of the associated orbital Feshbach resonance near $1300\mathrm{G}$. We measure the magnetic field dependence of the closed-channel dimer and of the open-channel pair state energy via clock-line spectroscopy in a deep optical lattice. In addition, we show that the free-to-bound transition into the dimer can be made first-order insensitive to the trap depth by the choice of lattice wavelength. Finally, we determine the fundamental intra- and interorbital scattering lengths and probe the stability of the corresponding pair states, finding long lifetimes in both interorbital interaction channels. These results are promising both for molecular clocks and for the preparation of strongly interacting multiorbital Fermi gases.

We report a time-resolved study on the electron kinetics and dynamics that occur during the formation of an ultracold plasma generated by resonance enhanced multiphoton ionization of krypton in a pulsed supersonic beam. Measurements are performed using a new apparatus that incorporates time-resolved velocity-mapped imaging of the entire electron energy distribution with nanosecond time resolution. We resolve the rapid deceleration and escape of 3.32 eV photoelectrons and the subsequent equilibration, cooling, and escape of electrons that are trapped by the expanding photocation distribution.