An ion trap is one of the most promising candidates for quantum computing. Current schemes mainly focus on a linear chain of up to about 100 ions in a Paul trap. To further scale up the qubit number, one possible direction is to use 2D or 3D ion crystals (Wigner crystals). In these systems, ions are generally subjected to large micromotion due to the strong fast-oscillating electric field, which can significantly influence the performance of entangling gates. In this paper, we develop an efficient numerical method to design high-fidelity entangling gates in a general 3D ion crystal. We present numerical algorithms to solve the equilibrium configuration of the ions and their collective normal modes. We then give a mathematical description of the micromotion and use it to generalize the gate scheme for linear ion chains into a general 3D crystal. The involved time integral of highly oscillatory functions is expanded into a fast-converging series for accurate and efficient evaluation and optimization. As a numerical example, we show a high-fidelity entangling gate design between two ions in a 100-ion crystal, with a theoretical fidelity above 99.9%.

It is known that distillation in continuous variable resource theories is impossible when restricted to Gaussian states and operations. To overcome this limitation, we enlarge the theories to include convex mixtures of Gaussian states and operations. This extension is operationally well motivated since classical randomness is easily accessible. We find that resource distillation becomes possible for convex Gaussian resource theories—albeit in a limited fashion. We derive this limitation by studying the convex roof extension of a Gaussian resource measure and then go on to show that our bound is tight by means of example protocols for the distillation of squeezing and entanglement.

We combine the Ramsey interferometry protocol, the Stern-Gerlach detection scheme, and the use of elongated geometry of a cloud of fully polarized cold cesium atoms to measure the selected component of the magnetic-field gradient along the atomic cloud in a single shot. In contrast to the standard method where the precession of two spatially separated atomic clouds is simultaneously measured to extract their phase difference, which is proportional to the magnetic-field gradient, we here demonstrate a gradiometer using a single image of an expanding atomic cloud with the phase difference imprinted along the cloud. Using resonant radio-frequency pulses and Stern-Gerlach imaging, we first demonstrate nutation and Larmor precession of atomic magnetization in an applied magnetic field. Next, we let the cold atom cloud expand in one dimension and apply the protocol for measuring the magnetic-field gradient. The resolution of our single-shot gradiometer is not limited by thermal motion of atoms and has an estimated absolute accuracy below $\pm 0.2$ mG/cm ($\pm 20$ nT/cm).

Accurate measurements of optical line broadening and microwave hyperfine transition shifts are essential for optimizing the performance of buffer-gas atomic clocks. Previous literature has reported inconsistent measurement values. We report measurements of the $D_1$ transition broadening and hyperfine frequency shift coefficients for ${}^{87}\mathrm{Rb}$ and ${}^{133}\mathrm{Cs}$ due to collisions with Ne and Ar atoms, as well as ${\mathrm{N}}_2$ molecules which is commonly employed for quenching in gas cell atomic clocks.

We investigate the quantum dynamics of ultra-long-range trilobite molecules exposed to homogeneous electric fields. A trilobite molecule consists of a Rydberg atom and a ground-state atom, which is trapped at large internuclear distances in an oscillatory potential due to scattering of the Rydberg electron off the ground-state atom. Within the Born-Oppenheimer approximation, we derive an analytic expression for the two-dimensional adiabatic electronic potential energy surface in weak electric fields valid up to 500 V/m. This is used to unravel the molecular quantum dynamics employing the multiconfigurational time-dependent Hartree method. Quenches of the electric field are performed to trigger the wave-packet dynamics including the case of field inversion. Depending on the initial wave packet, we observe radial intrawell and interwell oscillations as well as angular oscillations and rotations of the respective one-body probability densities. Opportunities to control the molecular configuration are identified, a specific example being the possibility to superimpose different molecular bond lengths by a series of periodic quenches of the electric field.

In this paper, we study the dynamics of a trapped atom interferometer with internal state labeling in the presence of interactions. We consider two situations: an atomic clock in which the internal states remain superposed, and an inertial sensor configuration in which they are separated. From the average spin evolution, we deduce the fringe contrast and the phase shift. In the clock configuration, we recover the well-known identical spin rotation effect (ISRE) which can significantly increase the spin coherence time. We also find that the magnitude of the effect depends on the trap geometry in a way that is consistent with our recent experimental results in a clock configuration [M. Dupont-Nivet, R. Demur, C. I. Westbrook, and S. Schwartz, New J. Phys. 20, 043051 (2018)], where ISRE was not observed. In the case of an inertial sensor, we show that despite the spatial separation it is still possible to increase the coherence time by using mean field interactions to counteract asymmetries of the trapping potential.

Helical structures like alpha helices, DNA, and microtubules have profound importance in biology. It has been suggested that these periodic arrangements of constituent units could support collective excitations similarly to crystalline solids. Here, we examine the interaction between such constructs and oscillating dipoles, and evaluate the role of the helicity in the coupling between electrodynamic fields and vibrations. Based on vibrational and eigenfunction analyses we identify a group of modes of coherent oscillations that give rise to a strong and delocalized response, selectivity in frequency, and a typical interaction range. To describe the field scattering due to the structure vibrations we consider an anisotropic permittivity with a helical periodicity, which applies to all vibration types and close dipole locations. The type of resonances identified here may help explain the role of electrodynamic fields in the diverse functionality of cytoskeletal microtubules in the cellular environment.

We propose a method of arbitrarily shaping and scaling the temporal intensity correlations of an optical signal locally, avoiding periodic correlations. We demonstrate our approach experimentally using stochastic intensity modulation. We also analyze and simulate shaping both temporal correlations and photon statistics that are fully specified by the user. We show that within the confines of monotony and convexity, the temporal correlations are independent of photon statistics and can take any shape.

Floquet-Magnus (FM) expansion theory is a powerful tool in periodically driven (Floquet) systems under high-frequency drives. In closed systems, it dictates that their stroboscopic dynamics under a time-periodic Hamiltonian is well captured by the FM expansion, which gives a static effective Hamiltonian. On the other hand, in dissipative systems driven by a time-periodic Liouvillian, it remains an important and nontrivial problem whether the FM expansion gives a static Liouvillian describing continuous-time Markovian dynamics, which we refer to as the “Liouvillianity” of the FM expansion. We answer this question for generic systems with local interactions. We find that while noninteracting systems can either break or preserve Liouvillianity of the FM expansion, generic few-body and many-body interacting systems break it under any finite drive, which is essentially caused by propagation of interactions via higher-order terms of the FM expansion. Liouvillianity breaking implies that Markovian dissipative Floquet systems in the high-frequency regimes do not have static (Markovian) counterparts, giving a signature of emergent non-Markovianity. Our theory provides a useful insight in the quest for unique phenomena in dissipative Floquet systems.

The low-energy electron-impact dissociation of molecular hydrogen has been a source of disagreement between various calculations and measurements for decades. Excitation of the ground state of ${\mathrm{H}}_2$ into the dissociative $b{}^3{\mathrm{\Sigma }}_u^{+}$ state is now well understood, with the most recent measurements being in excellent agreement with the molecular convergent close-coupling (MCCC) calculations of both integral and differential cross sections [Zawadzki et al., Phys. Rev. A 98, 062704 (2018)]. However, in the absence of similar measurements for vibrationally excited or isotopically substituted ${\mathrm{H}}_2$, cross sections for dissociation of these species must be determined by theory alone. We have identified large discrepancies between MCCC calculations and the recommended $R$-matrix cross sections for dissociation of vibrationally excited ${\mathrm{H}}_2$, ${\mathrm{D}}_2$, ${\mathrm{T}}_2$, HD, HT, and DT [Trevisan et al., Plasma Phys. Contr. Fusion 44 1263 (2002); Plasma Phys. Contr. Fusion 44, 2217 (2002)], with disagreement in both the isotope effect and dependence on initial vibrational level. Here we investigate the source of the discrepancies, and discuss the consequences for plasma models, which have incorporated the previously recommended data.

What does it take for real-deterministic $c$-valued (i.e., classical, commuting) variables to comply with the Heisenberg uncertainty principle? Here, we construct a class of real-deterministic $c$-valued variables out of the weak values obtained via a nonperturbing weak measurement of quantum operators with a postselection over a complete set of state vectors basis, which always satisfies the Kennard-Robertson-Schrödinger uncertainty relation. First, we introduce an auxiliary global random variable and couple it to the imaginary part of the weak value to convert the incompatibility between the quantum operator and the basis into the fluctuation of an “error term,” and then superimpose it onto the real part of the weak value. We show that this class of “$c$-valued physical quantities” provides a real-deterministic contextual hidden-variable model for the quantum expectation value of a certain class of operators. We then show that the Schrödinger and the Kennard-Robertson lower bounds can be obtained separately by imposing the classical uncertainty relation to the $c$-valued physical quantities associated with a pair of Hermitian operators. Within the representation, the complementarity between two incompatible quantum observables manifests the absence of a basis wherein the error terms of the associated two $c$-valued physical quantities simultaneously vanish. Furthermore, quantum uncertainty principle is captured by a specific irreducible epistemic restriction between the two $c$-valued physical quantities, foreign in classical mechanics, constraining the allowed form of their joint distribution. We then suggest an epistemic interpretation of the two terms decomposing the $c$-valued physical quantity as the optimal estimate under the epistemic restriction and the associated estimation error, and discuss the classical limit.

Amplitude-damping (AD) channels are good models for many physical scenarios, and so the development of protocols to discriminate between them is an important task in quantum information science. It is therefore important to bound the performance of such protocols. Since adaptivity has been shown to improve the performance of discrimination protocols, bounds on the distinguishability of AD channels must take this into account. In this paper, we use both channel simulation and a bound based on the diamond norm to significantly tighten the upper bound on the trace norm between the possible outputs of binary channel discrimination protocols acting on AD channels (and hence the lower bound on the error probability of such protocols). The diamond norm between any two AD channels is found analytically, giving the optimal error probability for a one-shot discrimination protocol. We also present a tighter lower bound on the achievable trace norm between protocol outputs (and a corresponding upper bound on the achievable error probability). The upper and lower bounds are compared with existing bounds and then applied to quantum hacking and biological quantum sensing scenarios.

A quantum cyclotron is one trapped electron or positron that occupies only its lowest cyclotron and spin states. A master equation is solved for a driven quantum cyclotron with a QND (quantum nondemolition) coupling to a detection oscillator in thermal equilibrium, the latter making this an open quantum system. The predicted rate of a cyclotron and spin quantum jumps as a function of drive frequency, for a small coupling between the detection motion and its thermal reservoir, differs sharply from what has been predicted and used for past measurements. The calculation suggests a ten times more precise electron magnetic moment measurement is possible, as needed to investigate current differences between the most precise prediction of the standard model of particle physics, and the most accurate measurement of a property of an elementary particle.

We develop a full multichannel spin model in momentum space to investigate three-body recombination of identical alkali-metal atoms colliding in a magnetic field. The model combines the exact three-atom spin structure and realistic pairwise atom-atom interactions. By neglecting the interaction between two particles when the spectating particle is not in its initial spin state we arrive at an approximate model. With this approximate model we achieve excellent agreement with the recent precise measurement of the ground Efimov resonance position in potassium-39 close to 33.58 G [R. Chapurin et al., Phys. Rev. Lett. 123, 233402 (2019)]. We analyze the limitations of our approximation by comparing to the numerical results for the full system and find that it breaks down for Feshbach resonances at larger magnetic fields in the same spin channel. There the relevant three-body closed channel thresholds are much closer to the open channel threshold, which enhances the corresponding multichannel couplings. Therefore the neglected components of the interaction should be included for those Feshbach resonances.

Since the construction of various topological photonic metamaterials, the Dirac degeneracy has been realized and provides a crucial opportunity to investigate the nonspecular effects [Goos-Hänchen (GH) and Imbert-Fedorov (IF) shifts] of light at the unique optical interface. In this paper, we furnish a general and precise model to explore how photonic Dirac point affects nonspecular effects in Dirac metamaterial. Based on this model, the giant nonspecular effects are discovered when a Gaussian beam reflects in the vicinity of a photonic Dirac point. We confirm that the giant nonspecular effects are the consequence of degeneracy between Brewster angles and critical angle caused by the Dirac point. Furthermore, the ability to generate a vortex beam at the Dirac point has also been simply verified. We believe that our work is of underlying significance, and may be served as a reference for the measurement of Dirac point, even other degenerate points. Moreover, our precise model can also be used to describe the nonspecular effects in other analogous photonic systems.

We study the polaritonic bandstructure of a two-dimensional (2D) atomic lattice coupled to a surface plasmon polariton mode in the single excitation regime. We adopt a Dirichlet-to-Neumann map based computational technique which can accurately model non-Markovian dynamics as well as narrow-bandwidth features associated with any periodic atom-photon system in general. Using this technique, we design a 2D atomic lattice using only two-level atoms, which has an isolated flat polaritonic band where the magnitude of the group velocity for the modes in the band approach zero across the whole Brillouin zone. Such a system could be employed to slow, store, and manipulate single photons in a 2D geometry.

Near-field interferometry with large dielectric nanoparticles opens the way to test fundamental modifications of standard quantum mechanics at an unprecedented level. We showcase the capabilities of such platform, in a state-of-the-art ground-based experimental setup, to set stringent bounds on the parameter space of collapse models and highlight the future perspectives for this class of experiments.

Continuous-variable (CV) entanglement is a valuable resource in the field of quantum information. One source of CV entanglement is the correlations between the position and momentum of photons in a two-mode squeezed state of light. In this paper, we theoretically study the generation of squeezed states, via spontaneous parametric down conversion, inside a two-mode lossy cavity that is pumped with a classical optical pulse. The dynamics of the density operator in the cavity is modeled using the Lindblad master equation, and we show that the solution to this model is the density operator for a two-mode squeezed thermal state, with a time-dependent squeezing amplitude and average thermal photon number for each mode. We derive an expression for the minimum correlation variance inside the cavity that depends crucially on the difference in the losses between the two modes. We apply our analytic solution to the important example of a microring resonator that is pumped with a Gaussian pulse. The expressions that we derive will help researchers optimize CV entanglement in lossy cavities.

We study the prospects of using the electric quadrupole transitions from the ground states of Cu, Ag, and Au to the metastable states ${}^{2}D_{5/2}$ as clock transitions in optical lattice clocks. We calculate lifetimes, transition rates, and systematic shifts and find that they are very suitable for this purpose. In particular, the elements are found to have a blackbody radiation shift that is one to two orders smaller than that of Sr. The Au clock is found to have strong sensitivities to a variation of the fine-structure constant, to effects of scalar dark matter, and to a violation of local Lorentz invariance (LLI). Cu and Ag are also suitable for tests of LLI. We identify two more metastable states (${}^{4}F_{9/2}^o$), one in Cu and another in Au, which can serve as additional clock transitions. The $\alpha$-sensitivity coefficients of the two Au clock transitions are large and have opposite sign. This doubles the overall sensitivity to variation of $\alpha$ and opens the possibility of a $\alpha$-variation test with a single neutral atomic species. We also present more accurate or additional values of the sensitivity to local position invariance violation for several established or proposed clock transitions. These values are important for properly evaluating the effectiveness of clock-clock comparisons.