Despite the increasing interest, the research field which studies the concepts of work and heat at the quantum level has suffered from two main drawbacks: first, the difficulty to properly define and measure the work, heat, and internal energy variation in a quantum system and, second, the lack of experiments. Here, we report a full characterization of the dissipated heat, work, and internal energy variation in a two-level quantum system interacting with an engineered environment. We use the IBMQ quantum computer to implement the driven system's dynamics in a dissipative environment. The experimental data allow us to construct quasiprobability distribution functions from which we recover the correct averages of work, heat, and internal energy variation in the dissipative processes. Interestingly, by increasing the environment coupling strength, we observe a reduction of the pure quantum features of the energy exchange processes that we interpret as the emergence of the classical limit. This makes the present approach a privileged tool to study, understand, and exploit quantum effects in energy exchanges.

Squeezing is a resource that enables precision enhancements in quantum metrology and can be used as a basis for the generation of entanglement by linear optics. While strong squeezing is challenging to generate in optical fields, here we present simple periodic modulation protocols in optomechanical systems that can generate large squeezing of their mechanical degrees of freedom for realistic system parameters. We then proceed to show how such protocols can serve to improve the measurement precision of weak forces and enhance the generation of entanglement between test masses that are subject to any kind of weak interaction. Moreover, these protocols can be reverted to reduce the amount of injected energy, while preserving the generated entanglement and making it more resilient to noise. We present the principle at work, discuss its application in a variety of physical settings, including levitated and tethered mechanical harmonic oscillators, and present example applications to Casimir and gravitational forces.

We consider strong two-body losses in bosonic gases trapped in one-dimensional optical lattices. We exploit the separation of timescales typical of a system in the many-body quantum Zeno regime to establish a connection with the theory of the time-dependent generalized Gibbs ensemble. Our main result is a simple set of rate equations that capture the simultaneous action of coherent evolution and two-body losses. This treatment gives an accurate description of the dynamics of a gas prepared in a Mott insulating state and shows that its long-time behavior deviates significantly from mean-field analyses. The possibility of observing our predictions in an experiment with ${}^{174}\mathrm{Yb}$ in a metastable state is also discussed.

In this letter we propose a method to realize a kind of spin-orbit coupling in ultracold Bose and Fermi gases that depends on the density of atoms. Our method combines two-photon Raman transition and periodical modulation of spin-dependent interaction, which gives rise to both the direct Raman process and the interaction-assisted Raman process. The interaction-assisted Raman process depends on the density of atoms. These two processes have opposite effects in terms of spin-momentum locking and compete with each other. As the interaction modulation increases, the system undergoes a crossover from the direct Raman process dominated regime to the interaction-assisted Raman process dominated regime. During this crossover, for bosons, both the condensate momentum and the chirality of condensate wave function change sign, and for fermions, the Fermi surface distortion is inverted. We highlight that there exists an emergent spatial reflectional symmetry in the crossover regime, which can manifest itself universally in both Bose and Fermi gases. Our method may pave a way to novel phenomena in the density-dependent spin-orbit coupling gauge field with intrinsic dynamics.

Sound propagation is a macroscopic manifestation of the interplay between the equilibrium thermodynamics and the dynamical transport properties of fluids. Here, for a two-dimensional system of ultracold fermions, we calculate the first and second sound velocities across the whole BCS-BEC crossover, and we analyze the system response to an external perturbation. In the low-temperature regime we reproduce the recent measurements [Phys. Rev. Lett. 124, 240403 (2020)] of the first sound velocity, which, due to the decoupling of density and entropy fluctuations, is the sole mode excited by a density probe. Conversely, a heat perturbation excites only the second sound, which, being sensitive to the superfluid depletion, vanishes in the deep BCS regime and jumps discontinuously to zero at the Berezinskii-Kosterlitz-Thouless superfluid transition. A mixing between the modes occurs only in the finite-temperature BEC regime, where our theory converges to the purely bosonic results.

Although the time-dependent buildup processes of Autler-Townes splitting in attosecond transient absorption spectra have been observed in plenty of experiments, there still exists an open question of when the splitting is maximized, which tells us how fast the system responds to the pump field and how well the adiabatic following is in a slowly varying few-cycle laser pulse. In this Letter we work out a compact formula to quantify the buildup time of the Autler-Townes splitting, which is related to multiple timescales of the laser-atom system, e.g., the Rabi period, the laser cycle, and the pulse duration, according to a universal power law. This scaling law applies not only to singly excited states, but also to doubly excited states in which complex electron-electron interaction gets involved. Our findings have potential applications in calibrating the zero delay in a transient absorption spectroscopy.

We propose a scheme for trapped-atom interferometry using an interacting Bose-Einstein condensate. The condensate is controlled and spatially split into two confined external momentum modes through a series of Bragg pulses. The proposed scheme (i) allows the generation of large entanglement in a trapped-interferometer configuration via one-axis twisting dynamics induced by interatomic interaction and (ii) avoids the suppression of interactions during the interferometer sequence by a careful manipulation of the state before and after phase encoding. The interferometer can be used for the measurement of gravity with a sensitivity beyond the standard quantum limit.

We have performed single-active-electron numerical calculations of neon- and argonlike atoms interacting with short, intense, circularly polarized laser pulses at wavelengths between 10 nm and 1000 nm. Our results reveal a surprisingly large change by a factor of about 100 in the ionization ratio of electrons in initial states counter-rotating with respect to the field over corotating electrons in the previously unexplored intermediate few-photon ionization regime. The physical mechanism behind this observation is related to resonant enhanced ionization via states close in energy to the initial states. These doorway states are accessible exclusively from the initial state for counter-rotating electrons within the respective wavelength regime. The results may open a new route for controlling the generation of spin-polarized electrons by ultrashort laser pulses.

We report on direct feedback cooling of single nanoparticles in an optical lattice to near their motional ground state. We find that the laser phase noise triggers severe heating of nanoparticles' motion along the optical lattice. When the laser phase noise is decreased by orders of magnitude, the heating rate is reduced and accordingly the occupation number is lowered to about 3. We establish a model directly connecting the heating rate and the measured laser phase noise and elucidate that the occupation number under the lowest laser phase noise in our system is limited only by photon recoil heating. Our results show that the reduction of the laser phase noise near the oscillation frequency of nanoparticles is crucial for bringing them near the ground state and pave the way to sensitive accelerometers and quantum mechanical experiments with ultracold nanoparticles in an optical lattice.

A high index dielectric spherical particle supports the high-$Q$ resonant Mie modes that result in a regular series of sharp resonances in the radiation pressure. The presence of a perfectly conducting metal surface transforms the Mie modes into extremely high-$Q$ magnetic bonding or electric antibonding modes for the close approach of a sphere to a surface. We show that an electromagnetic plane wave with normal incidence results in repulsive or attractive resonant optical forces relative to a metal for the excitation of electric bonding or magnetic antibonding resonant modes, respectively. A magnitude of resonant optical forces reaches the order of 1 nN of magnitude for micron-sized silicon particles and a power of light $1\text{mW}/\mu {\text{m}}^2$ that exceeds the gravitational force by four orders. However, what is the most remarkable is there are steady positions for a sphere between the pulling and pushing forces that give rise to the resonant binding of the sphere to a metal surface.

The electronic structures of actinide systems are extremely complicated because of strong electron correlations and relativistic effects. The atomic actinide anion poses even more challenges for experimental and theoretical investigations due to the extra loosely bound electron. In this work, we report the electronic structure of ${\mathrm{U}}^{-}$ using the slow-electron velocity-map imaging method. The electron affinity of U was measured to be 314.97(9) meV. Two excited states of ${\mathrm{U}}^{-}$ were observed and their energies were determined to be 84(11) and 160(12) meV above its ground state, respectively. The present study provides convincing evidence that the transition between the first excited state and the ground state of ${\mathrm{U}}^{-}$ is electric dipole (E1) allowed.

We study three-body collisions within ultracold mixtures with resonant interspecies $p$-wave interactions. Our results for the three-body effective interaction strength and decay rate are crucial towards understanding the stability and lifetime of these dilute quantum fluids. On resonance, we find that a class of universal scattering pathways emerges, regardless of the details of the short-range interactions. This gives rise quite generally to a remarkable regime where three-body effective interactions dominate over both inelastic decay and two-body effective interactions. Additionally, we find a series of mass-ratio-dependent trimer resonances further from resonance.

Non-Hermitian topological systems are the newest additions to the growing field of topological matter. In this work, we report the light-driven exceptional physics in a multi-Weyl semimetal. The driving is not only a key ingredient to control the position of the exceptional contours (ECs); light also has the ability to generate new ECs. Interestingly, we also demonstrate topological charge distribution and Lifshitz transition, which are controllable by the driving field in such generated ECs. Our findings present a promising platform for the manipulation and control over exceptional physics in non-Hermitian topological matter.

Reconnecting vortices in a superfluid allows for the energy transfer between different length scales and its subsequent dissipation. The present picture assumes that the dynamics of a reconnection is driven mostly by the phase of the order parameter, and this statement can be justified in the case of Bose-Einstein Condensates (BECs), where vortices have a simple internal structure. Therefore, it is natural to postulate that the reconnection dynamics in the vicinity of the reconnection moment is universal. This expectation has been confirmed in numerical simulations for BECs and experimentally for the superfluid ${}^4\mathrm{He}$. Not much has been said about this relation in the context of Fermi superfluids. In this Letter, we aim to bridge this gap, and we report our findings, which reveal that the reconnection dynamics conforms with the predicted universal behavior across the entire BCS-BEC crossover. The universal scaling also survives for spin-imbalanced systems, where unpaired fermions induce a complex structure of the colliding vortices.

We investigate the Bose-Hubbard chain in the presence of nearest-neighbor pairing. The pairing term gives rise to an unusual gapped ${\mathbb{Z}}_2$ Ising phase that has number fluctuation but no off-diagonal long range order. This phase has a strongly correlated many-body doubly degenerate ground state which is effectively a gap-protected macroscopic qubit. In the strongly interacting limit, the system can be mapped onto an anisotropic transverse spin chain, which in turn can be mapped to the better-known fermionic sister of the paired Bose-Hubbard chain: the Kitaev chain which hosts zero-energy Majorana bound states. While corresponding phases in the fermionic and bosonic systems have starkly different wave functions, they share identical energy spectra. We describe a possible cold-atom realization of the paired Bose-Hubbard model in a biased zigzag optical lattice with reservoir-induced pairing, opening a possible route towards experimental Kitaev chain spectroscopy.

In this Letter, we analyze the quantum dynamics of the perceptron model: a particle is constrained on an $N$-dimensional sphere, with $N\to \infty$, and subjected to a set of randomly placed hard-wall potentials. This model has several applications, ranging from learning protocols to the effective description of the dynamics of an ensemble of infinite-dimensional hard spheres in Euclidean space. We find that the jamming transition with quantum dynamics shows critical exponents different from the classical case. We also find that the quantum jamming transition, unlike the typical quantum critical points, is not confined to the zero-temperature axis, and the classical results are recovered only at $T=\infty$. Our findings have implications for the theory of glasses at ultralow temperatures and for the study of quantum machine-learning algorithms.

We report on the observation of the spin-exchange dynamics of ${}^{171}\mathrm{Yb}$ atoms in the ground state ${}^1{S}_0$ and in the metastable state ${}^3{P}_0$. We implement the mixed-dimensional two-orbital system using near-resonant and magic-wavelength optical lattices, where the ${}^1{S}_0$ and ${}^3{P}_0$ atoms are itinerant in a one-dimensional tube and localized in three dimensions, respectively. By exploiting an optical Stern-Gerlach method, we observe the spin depolarization of the ${}^1{S}_0$ atoms induced by the spin-exchange interaction with the ${}^3{P}_0$ atom. Our work could pave the way to the quantum simulation of the Kondo effect.

Efficient error-mitigation techniques demanding minimal resources is key to quantum information processing. We propose a generic protocol to mitigate quantum errors using detection-based quantum autoencoders. In our protocol, the quantum data are compressed into a latent subspace while leaving errors outside, the latter of which is then removed by a measurement and postselection. Compared to previously developed methods, our protocol on the one hand requires no extra qubits, and on the other hand it has a near-optimal denoising power, in which under reasonable requirements all errors detected outside of the latent subspace can be removed, while those inside the subspace cannot be removed by any means. Our detection-based quantum autoencoders are therefore particularly useful for near-term quantum devices in which controllable qubits are limited while noise reduction is important.