Nonlocality sharing for a three-qubit system via multilateral sequential measurements was deeply discussed. Nonlocality sharing based on the multiple violations of Mermin-Ardehali-Belinskii-Klyshko (MABK) inequality in the trilateral sequential measurements scenario can be observed, where all of eight MABK inequalities can be violated simultaneously. Nevertheless, the genuine nonlocality sharing based on the multiple violation of Svetlichny inequality can be only observed in the unilateral sequential measurements scenario. Compared with two-qubit cases, the nonlocality sharing in a three-qubit system shows more fruitful characteristics.

The information content of a source is defined in terms of the minimum number of bits needed to store the output of the source in a perfectly recoverable way. A similar definition can be given in the case of quantum sources, with qubits replacing bits. In the mentioned cases the information content can be quantified through Shannon's and von Neumann's entropy, respectively. Here we extend the definition of information content to operational probabilistic theories, and prove relevant properties such as the subadditivity and the relation between purity and information content of a state. We prove the consistency of the present notion of information content when applied to the classical and the quantum case. Finally, the relation with one of the notions of entropy that can be introduced in general probabilistic theories, the maximum accessible information, is given in terms of a lower bound.

We present an arithmetic circuit performing constant modular addition having $O\left(n\right)$ depth of Toffoli gates and using a total of $n+3$ qubits. This is an improvement by a factor of two compared to the width of the state-of-the-art Toffoli-based constant modular adder. The advantage of our adder, compared to the ones operating in the Fourier basis, is that it does not require small-angle rotations and their $\text{Clifford}+T$ decomposition. Our circuit uses a recursive adder combined with the modular addition scheme proposed by Vedral et al. The circuit is implemented and verified exhaustively with quantify, an open-sourced framework. We also report on the $\text{Clifford}+T$ cost of the circuit.

We theoretically analyze phase sensitivity using a parity-detection-based Mach-Zehnder interferometer (MZI) with the input states generated by performing non-Gaussian operations, viz., photon subtraction, photon addition, and photon catalysis, on a two-mode squeezed vacuum (TMSV) state. Since these non-Gaussian operations are probabilistic, it is of utmost importance to take the success probability into account. To this end, we consider a realistic model of photon subtraction, addition, and catalysis and derive a single expression of the Wigner function for photon subtracted, added, and catalyzed TMSV states. The Wigner function is used to evaluate the lower bound on the phase sensitivity via quantum Cramér-Rao bound and parity-detection-based phase sensitivity in the MZI. We identify the ranges of squeezing and transmissivity parameters where the non-Gaussian states provide better phase sensitivity than the TMSV state. Taking the success probability into account, it turns out that the photon addition is the most advantageous among all three non-Gaussian operations. We hope that the generalized Wigner function derived in this paper will be useful in various quantum information protocols and state characterization.

Neutral alkaline earth(like) atoms have recently been employed in atomic arrays with individual readout, control, and high-fidelity Rydberg-mediated entanglement. This emerging platform offers a wide range of new quantum science applications that leverage the unique properties of such atoms: ultranarrow optical “clock” transitions and isolated nuclear spins. Specifically, these properties offer an optical qubit ($o$) as well as ground ($g$) and metastable ($m$) nuclear spin qubits, all within a single atom. We consider experimentally realistic control of this omg architecture and its coupling to Rydberg states for entanglement generation, focusing specifically on ytterbium-171 (${}^{171}\mathrm{Yb}$) with nuclear spin $I=\frac{1}{2}$. We analyze the $S$-series Rydberg states of ${}^{171}\mathrm{Yb}$, described by the three spin-$\frac{1}{2}$ constituents (two electrons and the nucleus). We confirm that the $F=\frac{3}{2}$ manifold, a unique spin configuration, is well suited for entangling nuclear spin qubits. Further, we analyze the $F=\frac{1}{2}$ series, described by two overlapping spin configurations, using a multichannel quantum defect theory. We study the multilevel dynamics of the nuclear spin states when driving the clock or Rydberg transition with Rabi frequency ${\mathrm{\Omega }}_c=2\pi \times 200\text{kHz}$ or ${\mathrm{\Omega }}_R=2\pi \times 6\text{MHz}$, respectively, finding that a modest magnetic field ($\approx 200\text{G}$) and feasible laser polarization intensity purity ($\lesssim 0.99$) are sufficient for gate fidelities exceeding 0.99. We also study single-beam Raman rotations of the nuclear spin qubits and identify a “magic” linear polarization angle with respect to the magnetic field at which purely ${\sigma }_x$ rotations are possible.

Engineering a stationary entanglement between atoms or ions placed at small distances is a challenging problem in quantum information science. In this paper, the stationary and dynamics of entanglement in a system of dipole-coupled qubits interacting with a single-mode optical cavity in the strong coupling regime are theoretically investigated. We find that the entanglement in the steady state can be induced and tuned in nonresonance cases by considering the dipole-dipole interaction (DDI) between the qubits. We also point out that the novel measure used in this study can quantify the net multiqubit entanglement in the system. By increasing the DDI intensity, the behavior of the system depends on the number of qubits. Interestingly, with only two qubits, the amounts of steady-state entanglement enhances as the DDI intensity increases. For a system with more than two qubits, we find that DDI in the weak range of intensity plays a constructive role in the entanglement between qubits. However, it could destroy the stationary entanglement as the interaction between qubits intensifies. The entanglement of a system consisting of more than two qubits tends to disappear for an ensemble of qubits with smaller interatomic distances that lead to stronger dipolar interaction between nonadjacent qubits. Finally, we study the atomic population transfer as well as the transmitted spectrum.

The neutron electric dipole moment experiment at the Spallation Neutron Source (nEDM@SNS experiment) proposes to measure the nEDM using the spin-dependent capture cross section of neutrons on ${}^3\mathrm{He}$. The critical dressing mode of this experiment uses an oscillating magnetic field to dress the gyromagnetic ratios of neutrons and ${}^3\mathrm{He}$ to the same value. While this technique grants increased sensitivity to the nEDM by improving the signal-to-noise ratio, this mode of measurement also introduces additional noise from the power supply used to drive the dressing field. This can lead to randomly fluctuating magnetic fields which cause the spins of neutrons and ${}^3\mathrm{He}$ to drift apart over time. Here we use second-order time-dependent perturbation theory to compute relaxation and frequency shifts due to fluctuations in the dressing field in terms of the magnetic field noise power spectrum and compare these calculations to numerical solutions obtained by integrating the Bloch equations. We then use these results to develop mitigation strategies for this type of noise. Furthermore, we report on spin dressing modulation techniques that significantly amplify coherence times for the critically dressed system, and attempt to quantify the achievable coherence time.

An on-chip multigrating device is proposed to interface single atoms and integrated photonic circuits, by guiding and focusing lasers to the area $\sim 10 \mu \mathrm{m}$ above the chip for trapping, state manipulation, and readout of single rubidium atoms. For the optical dipole trap, two 850-nm laser beams are diffracted and overlapped to form the lattice of a single-atom dipole trap, with the diameter of the optical dipole trap being around 2.7 $\mu \mathrm{m}$. Similar gratings are designed for guiding a 780-nm probe laser to excite and also collect the fluorescence of ${}^{87}\mathrm{Rb}$ atoms. Such a device provides a compact solution for future applications of single atoms, including the single-photon source, single-atom quantum register, and single-atom quantum sensor.

In this work, we use Wannier functions to analyze topological phase transitions in one-dimensional photonic crystals. We first review the construction of exponentially localized Wannier functions in one dimension, and show how to numerically construct them for photonic systems. We then apply these tools to study a photonic analog of the Su-Schrieffer-Heeger model. We use photonic Wannier functions to construct a quantitatively accurate approximate model for the topological phase transition, and compute the localization of topological defect states. Finally, we discuss the implications of our work for the study of band representations for photonic crystals.

Chirp effects caused by the group delay dispersion (GDD) of optical pulses have a twofold meaning when applied to femtosecond stimulated Raman scattering (fs SRS). On the one hand, these effects are responsible for Raman mode modulation and are thus detrimental to the reconstruction of Raman spectra. On the other, they can be cleverly employed to turn GDD into an additional optical variable of great usefulness. Here, to master the whole subject, the classical approach to coherent Raman scattering is chosen for its simplicity and, with reference to a large class of measurements where electronically off-resonant Raman transitions are probed, fs SRS signals are readily found for linearly chirped Gaussian pulses that guarantee the solution to the nonlinear optical scattering problem without recourse to numerical methods. Thanks to this result, fundamental features of chirp-dependent fs SRS are explored by means of comparisons with experiments taken from the existing literature on the subject. The focus is on four fundamental manifestations of chirp dependence. They are (1) temporal resolution invariance in time modulation of Raman decay and its drift, (2) spectral focusing in Raman gain and loss, (3) line intensity modulation and Raman mode selection, and (4) single-shot time mapping of molecular dynamics. The findings of this work show that basic chirp-dependent Raman theory provides the necessary insights into the Raman phenomena appearing when chirp affects the laser pulses even in the extreme regime where the transform-limited fs pulse duration is just a few harmonic cycles of the laser fields.

We report on a scheme for laser cooling of ${}^{12}{\mathrm{C}}_2$. We have calculated the branching ratios for cycling and repumping transitions and calculated the number of photon scatterings required to achieve deflection and laser cooling of a beam of ${\mathrm{C}}_2$ molecules under realistic experimental conditions. Our results demonstrate that ${\mathrm{C}}_2$ cooling using the Swan ($d{}^3{\mathrm{\Pi }}_{\text{g}}\leftrightarrow a{}^3{\mathrm{\Pi }}_{\text{u}}$) and so-called Duck ($d{}^3{\mathrm{\Pi }}_{\text{g}}\leftrightarrow c{}^3{\mathrm{\Sigma }}_{\text{u}}^{+}$) bands is achievable via techniques similar to state-of-the-art molecular cooling experiments. The Phillips ($A{}^1{\mathrm{\Pi }}_{\text{u}}\leftrightarrow X{}^1{\mathrm{\Sigma }}_{\text{g}}^{+}$) and Ballik-Ramsay ($b{}^3{\mathrm{\Sigma }}_{\text{g}}^{-}\leftrightarrow a{}^3{\mathrm{\Pi }}_{\text{u}}$) bands offer the potential for narrow-line cooling. This work opens up a path to cooling of molecules with carbon-carbon bonds and may pave the way toward quantum control of organic molecules.

The emergence of an objective reality in line with the laws of the microscopic world has been the focus of longstanding debates. Recent approaches seem to have reached a consensus at least with respect to one aspect, namely, that the encoding of information about a given observable in a physical degree freedom is a necessary condition for such an observable to become an element of the physical reality. Taking this as a fundamental premise and inspired by quantum information theory, here we build an axiomatization for quantum realism—a notion of realism compatible with quantum theory. Our strategy consists of listing some physically motivated principles able to characterize quantum realism in a “metric” independent manner. We introduce some criteria defining monotones and measures of realism and then search for potential candidates within some celebrated information theories—those induced by the von Neumann, Rényi, and Tsallis entropies. We explicitly construct some classes of entropic quantifiers, among which some are shown to satisfy all the proposed axioms and hence can be taken as faithful estimates for the degree of reality (or definiteness) of a given physical observable. Hopefully, our framework may offer a formal ground for further discussions on foundational aspects of quantum mechanics.

We develop a general theory describing the thermodynamical behavior of open quantum systems coupled to thermal baths beyond perturbation theory. Our approach is based on the exact time-local quantum master equation for the reduced open-system states, and on a principle of minimal dissipation. This principle leads to a unique prescription for the decomposition of the master equation into a Hamiltonian part representing coherent time evolution and a dissipator part describing dissipation and decoherence. Employing this decomposition we demonstrate how to define work, heat, and entropy production, formulate the first and second laws of thermodynamics, and establish the connection between violations of the second law and quantum non-Markovianity.

Shortcuts to adiabaticity constitute a powerful alternative that speed up time evolution while mimicking adiabatic dynamics. In this paper we describe how to implement shortcuts to adiabaticity for the case of a massless scalar field inside a cavity with a moving wall, in $1+1$ dimensions. The approach is based on the known solution to the problem that exploits the conformal symmetry, and the shortcuts take place whenever there is no dynamical Casimir effect. We obtain a fundamental limit for the efficiency of an Otto cycle with the quantum field as a working system, that depends on the maximum velocity that the mirror can attain. We describe possible experimental realizations of the shortcuts using superconducting circuits.

We investigate competing entanglement dynamics in an Ising spin chain coupled to an external central ancilla qudit. In studying the real-time behavior following a quench from an unentangled spin-ancilla state, we find that the ancilla entanglement entropy $S_{vN;\mathcal{A}}$ tracks the dynamical phase transition in the underlying spin system. In this composite setting, purely spin-spin entanglement metrics such as mutual information and quantum Fisher information (QFI) decay as the ancilla entanglement entropy grows. We define multipartite entanglement loss (MEL) as the difference between collective magnetic fluctuations and QFI, which is zero in the pure spin chain limit. MEL directly quantifies the ancilla's effect on the development of spin-spin entanglement. One of our central results is that we find $M_{el}\left(t\right)\propto e^{S_{vN;\mathcal{A}}\left(t\right)}$. Our results provide a platform for exploring composite system entanglement dynamics and suggest that MEL serves as a quantitative estimate of information entropy shared between collective spins and the ancilla qudit. Our results present a framework that connects physical spin fluctuations, QFI, and bipartite entanglement entropy between collective quantum systems.

Quantum memory is a fundamental building block for large-scale quantum networks. On-demand optical storage with a large bandwidth, a high multimode capacity, and an integrated structure simultaneously is crucial for practical application. However, this has not been demonstrated yet. Here, we fabricate an on-chip waveguide in a ${}^{151}\mathrm{Eu}^{3+}:{\mathrm{Y}}_2{\mathrm{SiO}}_5$ crystal with insertion losses of 0.2 dB, and propose a pumping scheme to enable spin-wave atomic frequency comb (AFC) storage with a bandwidth of 11 MHz inside the waveguide. Based on this, we demonstrate the storage of 200 temporal modes using the AFC scheme and conditional on-demand storage of 100 temporal modes using the spin-wave AFC scheme. The interference visibility between the readout light field and the reference light field is $99.0\%\pm 0.6\%$ and $97\%\pm 3\%$ for AFC and spin-wave AFC storage, respectively, indicating the coherent nature of this low-loss, multimode, and integrated storage device.

Accurate population transfer of uncoupled or weakly coupled spin states is crucial for many quantum-information-processing tasks. In this paper, we propose a fast and robust scheme for population transfer which combines invariant-based inverse engineering and geometric formalism for robust quantum control. Our scheme is not constrained by the adiabatic condition and therefore can be implemented quickly. It can also effectively suppress the dominant noise in spin systems, which together with the fast feature guarantees the accuracy of the population transfer. Moreover, the control parameters of the driving Hamiltonian in our scheme are easy to design because they correspond to the curvature and torsion of a three-dimensional visual space curve derived by using geometric formalism for robust quantum control. We test the efficiency of our scheme by numerically simulating the ground-state population transfer in ${}^{15}\mathrm{N}$ nitrogen-vacancy centers and comparing our scheme with stimulated Raman transition, stimulated Raman adiabatic passage, and conventional shortcuts to adiabaticity based schemes, three types of schemes popularly used for population transfer. The numerical results clearly show that our scheme is advantageous over these previous ones.

It is known that a party with access to a Deutschian closed timelike curve (DCTC) can perfectly distinguish multiple nonorthogonal quantum states. In this paper we propose a practical method for discriminating multiple nonorthogonal states, by using a previously known quantum circuit designed to simulate DCTCs. This method relies on multiple copies of an input state, multiple iterations of the circuit, and a fixed set of unitary operations. We first characterize the performance of this circuit and study its asymptotic behavior. We also show how it can be equivalently recast as a local adaptive circuit that may be implemented simply in an experiment. Finally, we prove that our state discrimination strategy achieves the multiple Chernoff bound when discriminating an arbitrary set of pure qubit states.

The quantum regression formula for an open quantum system consists in an infinite hierarchy of conditions for its multitime correlation functions, thus requiring full access to the total “$\mathrm{system}+\mathrm{environment}$” evolution, and providing a stronger requirement than completely positive (CP) divisibility. Here, we analyze CP divisibility and check the validity of quantum regression beyond the Born-Markov approximation (e.g., the weak-coupling limit) for a class of generalized spin-boson models giving rise to a multilevel amplitude-damping evolution; in all cases, it is possible to engineer the system-bath coupling in such a way that quantum regression is exactly satisfied.

We consider a nanostructure consisting of a semiconductor quantum dot coupled to a metal nanoparticle, and we show with numerical simulations that the exciton state of the quantum dot can be robustly generated from the ground state even for small interparticle distances, using conventional chirped pulses with a Gaussian envelope. The asymmetry observed in the final exciton population with respect to the chirp sign of the applied pulses is explained using the nonlinear density matrix equations describing the system and is attributed to the real part of the parameter emerging from the interaction between excitons in the quantum dot and plasmons in the metal nanoparticle. The simplicity of Gaussian chirped pulses, which can also be easily implemented in the laboratory, makes the proposed robust quantum control scheme potentially useful for the implementation of ultrafast nanoswitches and quantum information processing tasks with semiconductor quantum dots.