Pure-state entanglement transformations have been thought of as irreversible, with reversible transformations generally only possible in the limit of many copies. Here, we show that reversible entanglement transformations do not require processing on the many-copy level but can instead be undertaken on individual systems, provided the amount of entanglement which is produced or consumed is allowed to fluctuate. We derive necessary and sufficient conditions for entanglement manipulations in this case. As a corollary, we derive an equation which quantifies the fluctuations of entanglement, which is formally identical to the Jarzynski fluctuation equality found in thermodynamics. One can also relate a forward entanglement transformation to its reverse process in terms of the entanglement cost of such a transformation, in a manner equivalent to the Crooks relation. We show that a strong converse theorem for entanglement transformations is formally related to the second law of thermodynamics, while the fact that the Schmidt rank of an entangled state cannot increase is related to the third law of thermodynamics. Achievability of the protocols is done by introducing an entanglement battery, a device which stores entanglement and uses an amount of entanglement that is allowed to fluctuate but with an average cost which is still optimal. This allows us to also solve the problem of partial entanglement recovery, and in fact, we show that entanglement is fully recovered. Allowing the amount of consumed entanglement to fluctuate also leads to improved and optimal entanglement dilution protocols.

Generation of quantum correlations between separate objects is of significance both in fundamental physics and in quantum networks. One important challenge is to create the directional “spooky action-at-a-distance” effects that Schrödinger called “steering” between two macroscopic and massive objects. Here, we analyze a generic scheme for generating steering correlations in cascaded hybrid systems in which two distant oscillators with effective masses of opposite signs are coupled to a unidirectional light field, a setup which is known to build up quantum correlations by means of quantum back-action evasion. The unidirectional coupling of the first to the second oscillator via the light field can be engineered to enhance steering in both directions and provides an active method for controlling the asymmetry of steering. We show that the resulting scheme can efficiently generate unconditional steady-state Einstein-Podolsky-Rosen steering between the two subsystems, even in the presence of thermal noise and optical losses. As a scenario of particular technological interest in quantum networks, we use our scheme to engineer enhanced steering from an untrusted node with limited tunability (in terms of interaction strength and type with the light field) to a trusted, highly tunable node, hence offering a path to implementing one-sided device-independent quantum tasks.

We present a device-independent quantum secret sharing scheme in arbitrary even dimension. We propose a $d$-dimensional $N$-partite linear game, utilizing a generic multipartite higher-dimensional Bell inequality, a generalization of Mermin's inequality in a higher dimension. The probability of winning this linear game defines the device-independence test in the proposed scheme. The security is proved under a causal independence assumption on measurement devices and it is based on the polygamy property of entanglement. By defining ${\epsilon }_{\mathrm{cor}}$ correctness and ${\epsilon }^c$ completeness for a quantum secret sharing scheme, we also show that the proposed scheme is ${\epsilon }_{\mathrm{cor}}$ correct and ${\epsilon }^c$ complete.

Simulating complex many-body quantum phenomena is a major scientific impetus behind the development of quantum computing, and a range of technologies are being explored to address such systems. We present the results of the largest photonics-based simulation to date, applied in the context of subatomic physics. Using an all-optical quantum frequency processor, the ground-state energies of light nuclei including the triton (${}^3\mathrm{H}$), ${}^3\mathrm{He}$, and the alpha particle (${}^4\mathrm{He}$) are computed. Complementing these calculations and utilizing a 68-dimensional Hilbert space, our photonic simulator is used to perform subnucleon calculations of the two- and three-body forces between heavy mesons in the Schwinger model. This work is a first step in simulating subatomic many-body physics on quantum frequency processors—augmenting classical computations that bridge scales from quarks to nuclei.

The orbital angular momentum of light, unlike spin, is an infinite-dimensional discrete variable and may hence offer enhanced performances for encoding, transmitting, and processing quantum information. Hitherto, this degree of freedom of light has been studied mainly in the context of quantum states with definite number of photons. On the other hand, field-quadrature continuous-variable quantum states of light allow implementing many important quantum protocols not accessible with photon-number states. Here, we realize a scheme based on a $q$-plate device for endowing a bipartite continuous-variable Gaussian entangled state with nonzero orbital angular momentum. We then apply a reconfigurable homodyne detector working directly with such nonzero orbital angular momentum modes in order to retrieve experimentally their entire quantum-state covariance matrix, thus providing a full characterization of their quantum fluctuation properties. Our work is a step towards generating multipartite continuous-variable entanglement in a single optical beam.

Common features are identified in the properties of the pure (PF) and ensemble (EF) energy functionals defined within the density matrix functional theory (DMFT) as well as their free-form (FFF) approximations. These features rationalize abandoning, in the common DMFT practice, prohibitively complicated generalized Pauli constraints (GPCs). Specifically, it is shown that the exact PF and EF coincide on the set of the $v$-representable first-order reduced density matrices (1RDMs), while FFFs approximate the common PF and EF for such 1RDMs. It is revealed that for some types of FFFs, for example for the geminal-based approximations, the GPCs are essentially trivialized to the pairwise natural occupation numbers (NONs) degeneracy conditions, routinely imposed for closed-shell systems.

We investigate two-frequency photoassociation of a weakly bound molecular state, focusing on a regime where the AC Stark shift is comparable to the halo-state energy. In this “high-intensity” regime, we observe features absent in low-intensity two-frequency photoassociation. We experimentally measure the spectra of ${}^{86}\mathrm{Sr}$ atoms coupled to the least bound state of the ${}^{86}\mathrm{Sr}_2$ ground electronic channel through an intermediate electronically excited molecular state. We compare the spectra to a simple three-level model that includes a two-frequency drive on each leg of the transition. With numerical solution of the time-dependent Schrödinger equation, we show that this model accurately captures (1) the existence of experimentally observed satellite peaks that arise from nonlinear processes, (2) the locations of the two-photon peak in the spectrum, including AC Stark shifts, and (3) in some cases, spectral line shapes. To better understand these numerical results, we develop an approximate treatment of this model, based on Floquet and perturbation theory, that gives simple formulas that accurately capture the halo-state energies. We expect these expressions to be valuable tools to analyze and guide future two-frequency photoassociation experiments.

We report the results of experiments in which positronium (Ps) atoms, optically excited to Rydberg-Stark states with principal quantum numbers ranging from $n=13$ to 19, were transported along the axis of a multiring electrode structure. By applying alternate positive and negative potentials to the ring electrodes, inhomogeneous electric fields suitable for guiding low-field-seeking atoms along the guide axis were generated. The multiring configuration used has the advantage that once the atoms are confined within it appropriate time-varying fields can be generated for deceleration and trapping. However, in this type of structure the possibility of nonadiabatic transitions of the fast (100 km/s) Ps atoms to unconfined high-field-seeking states exists. We show that for typical guiding fields this is not a significant loss mechanism and that efficient Ps transport can be achieved. Our data are in accordance with a Landau-Zener analysis of adiabatic transport through the field minima and Monte Carlo simulations that take into account Ps velocity distributions, electric dipole moments, and lifetimes, as well as the electric-field distributions in the guide.

We proposed a $\mathsf{Y}$-shaped molecular beam splitter for guided polar molecules, composed by several 1-μm-thick gold electrodes deposited on a chip. The splitter has a total length of 10 mm and the height of the electrostatic guiding center (minimum of the electric fields) is about 100 μm from the surface of the chip. Our theoretical analysis and trajectory calculations are carried out using two types of polar molecules of ammonia-${\mathrm{D}}_3$ ($\mathrm{N}{\mathrm{D}}_3$) and strontium fluoride (SrF). The calculated results show explicitly that, by applying a few hundred volts on the electrodes, the splitter can direct the guided (light or heavy) polar molecules to either of the two outgoing arms with any desired ratio (from 0% to 100%) by changing the voltages applied on the electrodes. This chip-scale molecular beam splitter offers a platform for molecular optics, precision measurements, and quantum computation. This basic optical element could be integrated into molecular chips and serve as a building block for a future gas-phase molecular laboratory on a chip.

We study the optical response of a two-dimensional (2D) square lattice of atoms using classical electrodynamics. Because of dipole-dipole interactions, the lattice atoms polarize as if the lattice were an atom with up to three resonance frequencies, with cooperatively shifted resonances and altered transition linewidths. We show that when the distance between two 2D lattices is large enough and Bragg reflections are absent, the lattices interact among themselves as if they radiated a plane wave whose amplitude is in accordance with the radiation from a dipole moment continuously distributed in the lattice plane. We employ these results to study light propagation in stacks of 2D lattices, drawing on simple qualitative pictures of the response of a 2D lattice and light propagation in one-dimensional (1D) waveguides. We show that a stack of 2D lattices may emulate regularly spaced atoms in a lossless 1D waveguide, and argue that in a suitable geometry the resonance shifts characteristic of 1D and 2D lattice structures may completely cancel to eliminate density-dependent resonance shifts of atoms bound to a three-dimensional (3D) lattice. A generalization to the case of anisotropic polarizability, such as in the presence of a magnetic field, reveals light frequencies induced by the magnetic field for which a 2D lattice is either completely transparent or completely opaque.

In this paper, we consider a two-component atomic Bose lattice gas inside an optical cavity to explore a competition between the short-range collisional and cavity-mediated long-range interactions. Utilizing a self-consistent mean-field approach, we map out the ground-state phase diagrams showing the superfluid, lattice supersolid, Mott insulator, and spin-density wave phases. Unlike its single-component analog, this lattice supersolid is here characterized by the coexistence of the superfluid and the spin-density wave. Moreover, for the relatively small long-range interaction, the phase diagrams exhibit a correspondence between the parity of the lattice filling number and the spin imbalance. Finally, we propose how to detect the different quantum phases under current experimental setups.

Atom interferometry with high visibility is of high demand for precision measurements. Here, a parallel multicomponent interferometer is achieved by preparing a spin-2 Bose-Einstein condensate of ${}^{87}\mathrm{Rb}$ atoms confined in a hybrid magneto-optical trap. After the preparation of a spinor Bose-Einstein condensate with spin degrees of freedom entangled, we observe four spatial interference patterns in each run of measurements corresponding to four hyperfine states we mainly populate in the experiment. The atomic populations in different Zeeman sublevels are made controllably using magnetic-field-pulse induced Majorana transitions. The spatial separation of atom cloud in different hyperfine states is reached by Stern-Gerlach momentum splitting. The high visibility of the interference fringes is reached by designing a proper overlap of the interfering wave packets. Due to uncontrollable phase accumulation in Majorana transitions, the phase of each individual spin is found to be subjected to unreproducible shift in multiple experimental runs. However, the relative phase across different spins is stable, paving a way towards noise-resilient multicomponent parallel interferometers.

We experimentally investigate the transfer of orbital angular momentum (OAM) of light in a solid driven by electromagnetically induced transparency (EIT). Under the condition of dynamical EIT, the OAM of the probe pulse is stored and retrieved in the experimental medium. By using a four-level double-lambda system to control the retrieval process of EIT storage, we show that OAM can be transferred from the probe field or the second control field to the newly generated signal field, which has a new spatial-frequency mode compared with the input mode. Furthermore, we use EIT-based four-wave mixing to investigate the direct OAM transfer without experiencing the storage, where we do not need to switch off and back on the control field.

We study the origin of the symmetry of the fluorescence spectrum from the two-level system subjected to a low-frequency periodic modulation and a near-resonant high-frequency monochromatic excitation using the analytical and numerical methods based on Floquet theory. We find that the fundamental origin of symmetry of the spectrum can be attributed to the presence of the generalized parity of the Floquet states, which depends on the driving parameters. The absence of the generalized parity can lead to the asymmetry of the spectrum. Based on the generalized parity, the conditions for the symmetry and asymmetry of the spectrum can be derived, which succeeds in predicting symmetry and asymmetry of the spectrum for the harmonic, biharmonic, and multiharmonic modulations. Moreover, we find that the secular approximation widely used in the analytical calculation may lead to artifact symmetry of the spectrum, which vanishes when such an approximation is avoided. The present study provides a significant perspective on the origin of the symmetry of the spectrum.

Wave-vector quasi-phase-matching was devised in the 1960s as a way to boost nonlinear interactions with efficient quantum noise squeezing as one outstanding outcome. In the era of quantum technologies, we propose a coupling quasi-phase-matching for efficient generation of multimode down-converted quantum light in nonlinear waveguide arrays. We highlight this technique achieving multimode quantum entanglement and Einstein-Podolsky-Rosen steering buildup. We discuss the feasibility of this method with current technology and demonstrate its competitiveness as a resource for continuous variables quantum information.

We study the energy structure and dynamics of a V-type three-level emitter embedded in a one-dimensional waveguide with model dispersion. Due to the presence of two different couplings between the upper levels and the waveguide modes, we find that the bound states in this system are quite different from the case of a two-level emitter. The energy structure is dependent on the relative position of the emitter's transition frequencies from the band with finite width. We obtain the phase diagrams through numerical analysis. The dynamics of spontaneous emission of the system is calculated exactly in the general case by means of the Green's function approach. The emitted photon is characterized by two components: a localized part and a traveling part, and the average frequency of the traveling part is different from that for resonant scattering. Through the quantum interference between the emitter's two transitions, it is found that the total excitation number of the localized photon and emitter can be greatly enhanced in some case in the spontaneous-emission process.

We explore whether localized surface plasmon polariton modes can transfer heat between molecules placed in the hot spot of a nanoplasmonic cavity through optomechanical interaction with the molecular vibrations. We demonstrate that external driving of the plasmon resonance indeed induces an effective molecule-molecule interaction corresponding to a heat transfer mechanism that can even be more effective in cooling the hotter molecule than its heating due to the vibrational pumping by the plasmon. This mechanism allows us to actively control the rate of heat flow between molecules through the intensity and frequency of the driving laser.

We propose a scheme to realize an optical Thirring model and create temporal optical Thirring solitons in a tripod-type atomic gas via double electromagnetically induced transparency (EIT). We show that giant enhancement of the cross-phase modulation for the two polarization components of the probe pulse can be obtained under the condition of the double EIT, and hence the optical Thirring model can be realized. We also show that the system supports stable temporal optical Thirring solitons, which have ultralow generation power and ultraslow propagation velocity. In particular, these temporal optical Thirring solitons may experience a significant Stern-Gerlach deflection when a gradient magnetic field is applied to the system. The results reported here are useful not only for extending the research realm of nonlinear magneto-optics but also for the application in precision measurements, such as the detection of microgradient magnetic fields.

In this work we derive ultrafast shortcuts for adiabatic rapid passage for a qubit where the only control variable is the longitudinal $z$ field, while the transverse $x$ field remains constant. This restrictive framework is pertinent to some important tasks in quantum computing, for example, the design of a high fidelity controlled-phase gate can be mapped to the adiabatic quantum control of such a qubit. We study this problem in the adiabatic reference frame and with appropriately rescaled time, using as control input the derivative of the total field polar angle (with respect to rescaled time). We first show that a constant pulse can achieve perfect adiabatic rapid passage at only specific times, corresponding to resonant shortcuts to adiabaticity. We next show that, by using “on-off-on-...-on-off-on” pulse sequences with appropriate characteristics (amplitude, timing, and number of pulses), a perfect fidelity can be obtained for every duration larger than the limit $\pi /\mathrm{\Omega }$, where $\mathrm{\Omega }$ is the constant transverse $x$ field. We provide equations from which these characteristics can be calculated. The proposed methodology for generalized resonant shortcuts exploits the advantages of composite pulses in the rescaled time, while the corresponding control $z$ field varies continuously and monotonically in the original time. Of course, as the total duration approaches the lower limit, the changes in the control signal become more abrupt. These results are not restricted only to quantum information processing applications, but is also expected to impact other areas, where adiabatic rapid passage is used.