Joao Barbosa, Jack C. Brennan, Alessandro Casaburi
et al.
One of the most important and topical challenges of quantum circuits is their scalability. Rapid single flux quantum (RSFQ) technology is at the forefront of replacing current standard CMOS-based control architectures for a number of applications, including quantum computing and quantum sensor arrays. By condensing the control and readout to single-flux-quantum-based on-chip devices that are directly connected to the quantum systems, it is possible to minimize the total system overhead, improving scalability and integration. In this article, we present a novel RSFQ device that generates multitone digital signals, based on complex pulse train sequences using a circular shift register (CSR) and a comb filter stage. We show that the frequency spectrum of the pulse trains is dependent on a preloaded pattern on the CSR, as well as on the delay line of the comb filter stage. By carefully selecting both the pattern and delay, the desired tones can be isolated and amplified as required. Finally, we propose architectures where this device can be implemented to control and read out arrays of quantum devices, such as qubits and single-photon detectors.
Atomic physics. Constitution and properties of matter, Materials of engineering and construction. Mechanics of materials
By employing singles, doubles, and triples excitations within the relativistic coupled-cluster framework, we perform comprehensive calculations of a wide range of atomic properties for the Th$^{3+}$ ion. These properties are essential for advancing nuclear clock technology and probing fundamental physics. Combining our isotope shift parameters with experimental data, we estimate highly accurate values of the differential nuclear charge radii for $^{232,229}$Th and $^{229m,229}$Th. Additionally, we determine the nuclear magnetic dipole and electric quadrupole moments for both the ground and isomeric states of $^{229}$Th by combining measured hyperfine structure constants with our theoretical calculations. Our precise evaluations of electric dipole polarizabilities and hyperfine-induced quadrupole moments are critical for assessing systematic uncertainties in $^{229}$Th$^{3+}$-based nuclear clock. Notably, we observe unexpectedly significant contributions from higher-order relativistic effects and excitations involving orbitals with higher angular momentum, which markedly influence the energies of the ground state and its fine-structure partner. These results highlight the substantial challenges in achieving highly accurate predictions for these properties.
This work deals with quantum transport in open quantum graphs. We consider the case of complete graphs on n vertices with an edge removed and attached to two leads to represent the entrance and exit channels, from where we calculate the transmission coefficient. We include the possibility of several vertices being connected or not and associate it with a randomization parameter p. To implement the calculation, we had to introduce the transmission coefficient of randomized quantum graphs, and we also proposed a procedure to obtain the exact and approximate but reliable results for such transmission coefficients. The main results show that transport is significantly affected by the removal of connections between pairs of vertices, but they also indicate the presence of a region where the transmission is fully suppressed, even when the number of edge removals is not too small.
Atomic physics. Constitution and properties of matter
The Mpemba effect (ME) refers to the surprising observation where, under certain conditions, a far-from-equilibrium state can relax toward equilibrium faster than a state closer to equilibrium. A paradigmatic example is provided by the curious fact that hot water can sometimes freeze faster than cold water. The ME has intrigued scientists for a long time and has been predicted and observed in a variety of classical and quantum systems. Recently, the search for Mpemba-like effects of purely quantum nature has raised a major interest. Here, we predict the emergence of ME in the quantum optics context exploiting non-classical states of light. By analyzing the decay dynamics of photon fields in a leaky optical resonator or waveguide, it is demonstrated that bosonic ME emerges in the context of the quantum nature of light. In particular, the relaxation dynamics are strongly influenced by the photon statistics of the initially trapped light field. The ME is observed when comparing the decay dynamics of classical light fields (coherent states) with certain non-classical states, such as Fock states, squeezed states, and Schrödinger cat states.
Atomic physics. Constitution and properties of matter
Abstract Motivated by recent advancements in theoretical and experimental studies of the high-energy excitations on an antiferromagnetic trimer chain, we numerically investigate the quantum phase transition and composite dynamics in this system by applying a magnetic field. The numerical methods we used include the exact diagonalization, density matrix renormalization group, time-dependent variational principle, and cluster perturbation theory. From calculating the entanglement entropy, we have revealed the phase diagram which includes the XY-I, 1/3 magnetization plateau, XY-II, and ferromagnetic phases. Both the critical XY-I and XY-II phases are characterized by the conformal field theory with a central charge c ≃ 1. By analyzing the dynamic spin structure factor, we elucidate the distinct features of spin dynamics across different phases. In the regime with weak intertrimer interaction, we identify the intermediate-energy and high-energy modes in the XY-I and 1/3 magnetization plateau phases as internal trimer excitations, corresponding to the propagating of doublons and quartons, respectively. Notably, applying a magnetic field splits the high-energy spectrum into two branches, labeled as the upper quarton and lower quarton. Furthermore, we explore the spin dynamics of a frustrated trimerized model closely related to the quantum magnet Na2Cu3Ge4O12. In the end, we extend our discuss on the possibility of the quarton Bose-Einstein condensation in the trimer systems. Our results are expected to be further verified through the inelastic neutron scattering and resonant inelastic X-ray scattering, and also provide valuable insights for exploring high-energy exotic excitations.
Materials of engineering and construction. Mechanics of materials, Atomic physics. Constitution and properties of matter
I consider the longstanding issue of the hermiticity of the Dirac equation in curved spacetime. Instead of imposing hermiticity by adding ad hoc terms, I renormalize the field by a scaling function, which is related to the determinant of the metric, and then regularize the renormalized field on a discrete lattice. I found that, for time-independent and diagonal (or conformally flat) coordinates, the Dirac equation returns a pseudo-Hermitian (i.e., PT-symmetric) Hamiltonian when properly regularized on the lattice. Notably, the PT-symmetry is unbroken, ensuring a real energy spectrum and unitary time evolution. This establishes stringent conditions for the existence of complex spectra in 1D non-Hermitian (NH) models. Conversely, time-dependent spacetime coordinates break pseudohermiticity, yielding NH Hamiltonians with nonunitary time evolution. Similarly, space-dependent coordinates lead to the NH skin effect (NHSE), i.e., the accumulation of localized states on the boundaries. Arguably, these NH effects are physical: time dependence leads to local gain and loss processes and nonunitary growth or decay. Conversely, space dependence leads to the NHSE with spatial decay of the fields in a preferential direction. In other words, the curvature gradients induce an imaginary gauge field, corresponding to a drift force acting in space and time, pushing the eigenmodes to the boundaries or forcing their probability density to increase or decrease over time. Hence, temporal curvature gradients produce nonunitary gain or loss, while spatial curvature gradients correspond to the NHSE, allowing for the description of these two phenomena in a unified framework. This also suggests a duality between NH physics and spacetime deformations, framing NH physics in purely geometric terms. This metric-induced nonhermiticity unveils an unexpected connection between the spacetime metric and NH phases of matter.
In the process of interatomic Coulombic electron capture, an incident free electron is captured at an atomic center $A$ and the transition energy is transferred radiationlessly over a rather large distance to a neighboring atom $B$ of different species, upon which the latter is ionized. We consider two-step cascade processes where the electron emitted from atom $B$ is subsequently captured as well, either at center $A$ or yet another atomic center $C$, leading to emission of a second electron from one of the centers. We derive formulas for the cross section of this double interatomic Coulombic electron capture and discuss the relevance of this process, which leads to a substantial rearrangement of the electronic configuration, in various two- and three-center atomic systems.
Abstract Magnetoelectric phenomena are intimately linked to relativistic effects and also require the material to break spatial inversion symmetry and time-reversal invariance. Magnetoelectric coupling can substantially affect light–matter interaction and lead to non-reciprocal light propagation. Here, we confirm on a fully experimental basis, without invoking either symmetry-based or material-specific assumptions, that the optical magnetoelectric effect in materials with non-parallel magnetization (M) and electric polarization (P) generates a trilinear term in the refractive index, δ n ∝ k ⋅ (P × M), where k is the propagation vector of light. Its sharp magnetoelectric resonances in the terahertz regime, which are simultaneously electric and magnetic dipole active excitations, make Co2Mo3O8 an ideal compound to demonstrate this fundamental relation via independent variation of M, P, and k. Remarkably, the material shows almost perfect one-way transparency in moderate magnetic fields for one of these magnetoelectric resonances.
Materials of engineering and construction. Mechanics of materials, Atomic physics. Constitution and properties of matter
Abstract Topological phonons in crystalline materials have been attracting great interest. Most cases studied so far are direct generalizations of the topological states from electronic systems. Here, we reveal a class of topological phonons - the symmetry-enforced nodal-chain phonons, which manifest the characteristic of phononic systems. We show that in five space groups with D 2d little co-group at a non-time-reversal-invariant-momentum point, the phononic nodal chain is guaranteed to exist owing to the vector basis symmetry of phonons, which is a character distinct from electronic and other systems. In other words, this symmetry enforcement feature of the proposed nodal chain is limited to phononic systems. Interestingly, the chains in these five space groups exhibit two different patterns: for tetragonal systems, they are one-dimensional along the fourfold axis; for cubic systems, they form a three-dimensional network structure. Based on first-principles calculations, we identify K2O as a realistic material hosting the proposed nodal-chain phonons. We show that the effect of LO-TO splitting helps to expose the nodal-chain phonons in a large frequency window. In addition, the nodal chains may lead to drumhead surface phonon modes on multiple surfaces of a sample.
Materials of engineering and construction. Mechanics of materials, Atomic physics. Constitution and properties of matter
Abstract We investigate the quantum dynamics of the antiferromagnetic transverse field Ising model on the triangular lattice through large-scale quantum Monte Carlo simulations and stochastic analytic continuation. This model effectively describes a series of triangular rare-earth compounds, for example, TmMgGaO4. At weak transverse field, we capture the excitations related to topological quantum strings, which exhibit continuum features described by XY chain along the strings and those in accord with ‘Luttinger string liquid’ in the perpendicular direction. The continuum features can be well understood from the perspective of topological strings. Furthermore, we identify the contribution of strings from the excitation spectrum. Our study provides characteristic features for the experimental search for string-related excitations and proposes a theoretical method to pinpoint topological excitations in the experimental spectra.
Materials of engineering and construction. Mechanics of materials, Atomic physics. Constitution and properties of matter
Abstract We consider a model of electrons at zero temperature, with a repulsive interaction which is a function of the energy transfer. Such an interaction can arise from the combination of electron–electron repulsion at high energies and the weaker electron–phonon attraction at low energies. As shown in previous works, superconductivity can develop despite the overall repulsion due to the energy dependence of the interaction, but the gap Δ(ω) must change sign at some (imaginary) frequency ω 0 to counteract the repulsion. However, when the constant repulsive part of the interaction is increased, a quantum phase transition towards the normal state occurs. We show that, as the phase transition is approached, Δ and ω 0 must vanish in a correlated way such that $$1/| \log [{{\Delta }}(0)]| \sim {\omega }_{0}^{2}$$ 1 / ∣ log [ Δ ( 0 ) ] ∣ ~ ω 0 2 . We discuss the behavior of phase fluctuations near this transition and show that the correlation between Δ(0) and ω 0 locks the phase stiffness to a non-zero value.
Materials of engineering and construction. Mechanics of materials, Atomic physics. Constitution and properties of matter
Abstract The quantum spin liquid candidate NaYbSe2 was recently reported to exhibit a Mott transition under pressure. Superconductivity was observed in the high-pressure metallic phase, raising the question concerning its relation with the low-pressure quantum spin liquid ground state. Here we combine the density functional theory and the dynamical mean-field theory to explore the underlying mechanism of the insulator-to-metal transition and superconductivity and establish an overall picture of its electronic phases under pressure. Our results suggest that NaYbSe2 is a charge-transfer insulator at ambient pressure. Upon increasing pressure, however, the system first enters a semi-metallic state with incoherent Kondo scattering against coexisting localized Yb-4f moments, and then turns into a heavy-fermion metal. In between, there may exist a delocalization quantum critical point responsible for the observed non-Fermi liquid region with linear-in-T resistivity. The insulator-to-metal transition is therefore a two-stage process. Superconductivity emerges in the heavy-fermion phase with well-nested Yb-4f Fermi surfaces, suggesting that spin fluctuations may play a role in the Cooper pairing. NaYbSe2 might therefore be the 3rd Yb-based heavy-fermion superconductor with a very “high” T c than most heavy-fermion superconductors.
Materials of engineering and construction. Mechanics of materials, Atomic physics. Constitution and properties of matter
Ramon W. J. Overwater, Masoud Babaie, Fabio Sebastiano
Quantum error correction (QEC) is required in quantum computers to mitigate the effect of errors on physical qubits. When adopting a QEC scheme based on surface codes, error decoding is the most computationally expensive task in the classical electronic back-end. Decoders employing neural networks (NN) are well-suited for this task but their hardware implementation has not been presented yet. This work presents a space exploration of fully connected feed-forward NN decoders for small distance surface codes. The goal is to optimize the NN for the high-decoding performance, while keeping a minimalistic hardware implementation. This is needed to meet the tight delay constraints of real-time surface code decoding. We demonstrate that hardware-based NN-decoders can achieve the high-decoding performance comparable to other state-of-the-art decoding algorithms whilst being well below the tight delay requirements <inline-formula><tex-math notation="LaTeX">$(\approx 440\ \text{ns})$</tex-math></inline-formula> of current solid-state qubit technologies for both application-specific integrated circuit designs <inline-formula><tex-math notation="LaTeX">$(< \!30\ \text{ns})$</tex-math></inline-formula> and field-programmable gate array implementations <inline-formula><tex-math notation="LaTeX">$(<\! 90\ \text{ns})$</tex-math></inline-formula>. These results indicate that NN-decoders are viable candidates for further exploration of an integrated hardware implementation in future large-scale quantum computers.
Atomic physics. Constitution and properties of matter, Materials of engineering and construction. Mechanics of materials
Neel Kanth Kundu, Matthew R. McKay, Ranjan K. Mallik
In this article, we propose a machine-learning framework for parameter estimation of single-mode Gaussian quantum states. Under a Bayesian framework, our approach estimates parameters of suitable prior distributions from measured data. For phase-space displacement and squeezing parameter estimation, this is achieved by introducing expectation–maximization (EM)-based algorithms, while for phase parameter estimation, an empirical Bayes method is applied. The estimated prior distribution parameters along with the observed data are used for finding the optimal Bayesian estimate of the unknown displacement, squeezing, and phase parameters. Our simulation results show that the proposed algorithms have estimation performance that is very close to that of “Genie Aided” Bayesian estimators, which assume perfect knowledge of the prior parameters. In practical scenarios, when numerical values of the prior distribution parameters are not known beforehand, our proposed methods can be used to find optimal Bayesian estimates from the observed measurement data.
Atomic physics. Constitution and properties of matter, Materials of engineering and construction. Mechanics of materials
Xue Zhang, Abhishek Banerjee, Mahapan Leyser
et al.
The effects of scalar and pseudoscalar ultralight bosonic dark matter (UBDM) were searched for by comparing the frequency of a quartz oscillator to that of a hyperfine-structure transition in $^{87}$Rb, and an electronic transition in $^{164}$Dy. We constrain linear interactions between a scalar UBDM field and Standard-Model (SM) fields for an underlying UBDM particle mass in the range $1\times10^{-17}-8.3\times10^{-13} $ eV and quadratic interactions between a pseudoscalar UBDM field and SM fields in the range $5\times10^{-18}- 4.1\times10^{-13} $ eV. Within regions of the respective ranges, our constraints on linear interactions significantly improve on results from previous, direct searches for oscillations in atomic parameters, while constraints on quadratic interactions surpass limits imposed by such direct searches as well as by astrophysical observations.
Nicolas Schierbaum, Johannes Rheinlaender, Tilman E. Schäffer
Combined AFM with TFM is a powerful tool to simultaneously and directly measure “passive” viscoelastic material properties and “active” contractile prestress of living cells at the nanoscale.
Interconnecting small quantum computers will be essential in the future for creating large-scale, robust quantum computers. Methods for distributing monolithic quantum algorithms efficiently are, thus, needed. In this article, we consider an approach for distributing the accelerated variational quantum eigensolver algorithm over arbitrary sized—in terms of number of qubits—distributed quantum computers. We consider approaches for distributing qubit assignments of the Ansatz states required to estimate the expectation value of Hamiltonian operators in quantum chemistry in a parallelized computation and provide a systematic approach to generate distributed quantum circuits for distributed quantum computing. Moreover, we propose an architecture for a distributed quantum control system in the context of centralized and decentralized network control.
Atomic physics. Constitution and properties of matter, Materials of engineering and construction. Mechanics of materials