José Ferreira Neto, Benedek Gaál, Luca Vannucci
et al.
We study the impact of mechanical vibrations on the performance of the photonic “hourglass” structure, which is predicted to emit single photons on demand with near-unity efficiency and indistinguishability. Previous investigations neglected the impact of vibrational modes inherent to this quasi-1D geometry, relying instead on a three-dimensional bulk assumption for the phonon modes. However, it has been shown that phonon decoherence has a much stronger impact on 1D structures as compared with bulk media. Here, we surprisingly demonstrate the robustness of the photonic hourglass design, achieving close-to-unity indistinguishability even by incorporating a detailed description of the vibrational modes. We explain this unexpected result in terms of the large Purcell enhancement of the hourglass single-photon source, which eliminates the negative effect of phonons. Our findings highlight the key role of high-Q optical cavities in mitigating the detrimental effect of phonon decoherence, even for structures of reduced dimensionality.
Atomic physics. Constitution and properties of matter
Shivendra Singh Parihar, Girish Pahwa, Baker Mohammad
et al.
Complementary metal–oxide–semiconductor (CMOS)-based computing promises drastic improvement in performance at extremely low temperatures (e.g., 77 K, 10 K). The field of extremely low temperature CMOS-environment-based computing holds the promise of delivering remarkable enhancements in both performance and power consumption. Static random access memory (SRAM) plays a major role in determining the performance and efficiency of any processor due to its superior performance and density. This work aims to reveal how extremely low temperature operations profoundly impact the existing well-known tradeoffs in SRAM-based memory arrays. To accomplish this, first, we measure and model the 5 nm fin field-effect transistors characteristics over a wide temperature range from 300 K down to 10 K. Next, we develop a framework to perform simulations on the SRAM array by varying the number of rows and columns for examining the influence of leakage current (<inline-formula><tex-math notation="LaTeX">$I$</tex-math></inline-formula><sub>leak</sub>) and parasitic effects of bit line (BL) and word line (WL) on the size and performance of the SRAM array under extremely low temperatures. For a comprehensive analysis, we further investigated the maximum attainable array size, extending our study down to 10 K, utilizing three distinct cell types. With the help of SRAM array simulations, we reveal that the maximum array size at extremely low temperatures is limited by WL parasitics instead of <inline-formula><tex-math notation="LaTeX">$I$</tex-math></inline-formula><sub>leak</sub>, and the performance of the SRAM is governed by BL and WL parasitics. In addition, we elucidate the influence of transistor threshold voltage (<inline-formula><tex-math notation="LaTeX">$V$</tex-math></inline-formula><sub>TH</sub>) engineering on the optimization of the SRAM array at extremely low temperature environments.
Atomic physics. Constitution and properties of matter, Materials of engineering and construction. Mechanics of materials
Abstract We combine ultra-high-resolution inelastic neutron scattering and quantum Monte Carlo simulations to study thermodynamics and spin excitations in the spin-supersolid phase of the triangular lattice XXZ antiferromagnet K2Co(SeO3)2 under zero and non-zero magnetic field. BKT transitions signaling the onset of Ising and supersolid order are clearly identified, and the Wannier entropy is experimentally recovered just above the supersolid phase. At low temperatures, with an experimental resolution of about 23 μeV, no discrete coherent magnon modes are resolved within a broad scattering continuum. Alongside gapless excitations, a pseudo-Goldstone mode with a 0.06 meV gap is observed. A second, higher-energy continuum replaces single-spin-flip excitations of the Ising model. Under applied fields, the continuum evolves into coherent spin waves, with Goldstone and pseudo-Goldstone sectors responding differently. The experiments and simulations show excellent quantitative agreement.
Materials of engineering and construction. Mechanics of materials, Atomic physics. Constitution and properties of matter
Bethany Davies, Thomas Beauchamp, Gayane Vardoyan
et al.
Quantum protocols commonly require a certain number of quantum resource states to be available simultaneously. An important class of examples is quantum network protocols that require a certain number of entangled pairs. Here, we consider a setting in which a process generates a quantum resource state with some probability <inline-formula><tex-math notation="LaTeX">$p$</tex-math></inline-formula> in each time step and stores it in a quantum memory that is subject to time-dependent noise. To maintain sufficient quality for an application, each resource state is discarded from the memory after <inline-formula><tex-math notation="LaTeX">$w$</tex-math></inline-formula> time steps. Let <inline-formula><tex-math notation="LaTeX">$s$</tex-math></inline-formula> be the number of desired resource states required by a protocol. We characterize the probability distribution <inline-formula><tex-math notation="LaTeX">$X_{(w,s)}$</tex-math></inline-formula> of the ages of the quantum resource states, once <inline-formula><tex-math notation="LaTeX">$s$</tex-math></inline-formula> states have been generated in a window <inline-formula><tex-math notation="LaTeX">$w$</tex-math></inline-formula>. Combined with a time-dependent noise model, knowledge of this distribution allows for the calculation of fidelity statistics of the <inline-formula><tex-math notation="LaTeX">$s$</tex-math></inline-formula> quantum resources. We also give exact solutions for the first and second moments of the waiting time <inline-formula><tex-math notation="LaTeX">$\tau _{(w,s)}$</tex-math></inline-formula> until <inline-formula><tex-math notation="LaTeX">$s$</tex-math></inline-formula> resources are produced within a window <inline-formula><tex-math notation="LaTeX">$w$</tex-math></inline-formula>, which provides information about the rate of the protocol. Since it is difficult to obtain general closed-form expressions for statistical quantities describing the expected waiting time <inline-formula><tex-math notation="LaTeX">$\mathbb {E}(\tau _{(w,s)})$</tex-math></inline-formula> and the distribution <inline-formula><tex-math notation="LaTeX">$X_{(w,s)}$</tex-math></inline-formula>, we present two novel results that aid their computation in certain parameter regimes. The methods presented in this work can be used to analyze and optimize the execution of quantum protocols. Specifically, with an example of a blind quantum computing protocol, we illustrate how they may be used to infer <inline-formula><tex-math notation="LaTeX">$w$</tex-math></inline-formula> and <inline-formula><tex-math notation="LaTeX">$p$</tex-math></inline-formula> to optimize the rate of successful protocol execution.
Atomic physics. Constitution and properties of matter, Materials of engineering and construction. Mechanics of materials
Abstract The incommensurate charge density wave states (CDWs) can exhibit steady motion in the flow limit after depinning, behaving as a nonequilibrium system with time-dependent states. Since the moving CDW, like an electric current, breaks both time-reversal and inversion symmetries, one may speculate the emergence of nonreciprocal nonlinear responses from such motion. However, the moving CDW order parameter is intrinsically time-dependent in the lab frame, and it is known to be challenging to evaluate the responses of such a time-varying system. In this work, following the principle of Galilean relativity, we resolve this time-dependent hard problem in the lab frame by mapping the system to the comoving frame with static CDW states through the Galilean transformation. We explicitly show that the nonreciprocal nonlinear responses would be generated by the movement of CDW states through violating Galilean relativity.
Materials of engineering and construction. Mechanics of materials, Atomic physics. Constitution and properties of matter
Leonardo Oleynik, Junaid Ur Rehman, Hayder Al-Hraishawi
et al.
This article explores the performance of quantum communication systems in the presence of noise and focuses on finding the optimal encoding for maximizing the classical communication rate, approaching the classical capacity in some scenarios. Instead of theoretically bounding the ultimate capacity of the channel, we adopt a signal processing perspective to estimate the achievable performance of a physically available but otherwise unknown quantum channel. By employing a variational algorithm to estimate the trace distance between quantum states, we numerically determine the optimal encoding protocol for the amplitude damping and Pauli channels. Our simulations demonstrate the convergence and accuracy of the method with a few iterations, confirming that optimal conditions for binary quantum communication systems can be variationally determined with minimal computation. Furthermore, since the channel knowledge is not required at the transmitter or at the receiver, these results can be employed in arbitrary quantum communication systems, including satellite-based communication systems, a particularly relevant platform for the quantum Internet.
Atomic physics. Constitution and properties of matter, Materials of engineering and construction. Mechanics of materials
The searching efficiency of the quantum approximate optimization algorithm is dependent on both the classical and quantum sides of the algorithm. Recently, a quantum approximate Bayesian optimization algorithm (QABOA) that includes two mixers was developed, where surrogate-based Bayesian optimization is applied to improve the sampling efficiency of the classical optimizer. A continuous-time quantum walk mixer is used to enhance exploration, and the generalized Grover mixer is also applied to improve exploitation. In this article, an extension of the QABOA is proposed to further improve its searching efficiency. The searching efficiency is enhanced through two aspects. First, two mixers, including one for exploration and the other for exploitation, are applied in an alternating fashion. Second, uncertainty of the quantum circuit is quantified with a new quantum Matérn kernel based on the kurtosis of the basis state distribution, which increases the chance of obtaining the optimum. The proposed new two-mixer QABOA's with and without uncertainty quantification are compared with three single-mixer QABOA's on five discrete and four mixed-integer problems. The results show that the proposed two-mixer QABOA with uncertainty quantification has the best performance in efficiency and consistency for five out of the nine tested problems. The results also show that QABOA with the generalized Grover mixer performs the best among the single-mixer algorithms, thereby demonstrating the benefit of exploitation and the importance of dynamic exploration–exploitation balance in improving searching efficiency.
Atomic physics. Constitution and properties of matter, Materials of engineering and construction. Mechanics of materials
Kavya Ravindran, Jayjit Kumar Dey, Aryan Keshri
et al.
Topological phenomena at the oxide interfaces attract the scientific community for the fertile ground of exotic physical properties and highly favorable applications in the area of high-density low-energy nonvolatile memory and spintronic devices. Synthesis of atomically controlled ultrathin high-quality films with superior interfaces and their characterization by high resolution experimental set up along with high output theoretical calculations matching with the experimental results make this field possible to explain some of the promising quantum phenomena and exotic phases. In this review, we highlight some of the interesting interface aspects in ferroic thin films and heterostructures including the topological Hall effect in magnetic skyrmions, strain dependent interlayer magnetic interactions, interlayer coupling mediated electron conduction, switching of noncollinear spin texture etc. Finally, a brief overview followed by the relevant aspects and future direction for understanding, improving, and optimizing the topological phenomena for next generation applications are discussed.
Atomic physics. Constitution and properties of matter, Materials of engineering and construction. Mechanics of materials
In superconducting quantum processors, the predictability of device parameters is of increasing importance as many laboratories scale up their systems to larger sizes in a 3-D-integrated architecture. In particular, the properties of superconducting resonators must be controlled well to ensure high-fidelity multiplexed readout of qubits. Here, we present a method, based on conformal mapping techniques, to predict a resonator's parameters directly from its 2-D cross-section, without computationally heavy and time-consuming 3-D simulation. We demonstrate the method's validity by comparing the calculated resonator frequency and coupling quality factor with those obtained through 3-D finite-element-method simulation and by measurement of 15 resonators in a flip-chip-integrated architecture. We achieve a discrepancy of less than 2% between designed and measured frequencies for 6-GHz resonators. We also propose a design method that reduces the sensitivity of the resonant frequency to variations in the interchip spacing.
Atomic physics. Constitution and properties of matter, Materials of engineering and construction. Mechanics of materials
The problem of identifying the sensitivity of living organisms to ionizing irradiation remains relevant, considering the spread of anthropogenic environmental pollution. The study on the effect of single X-ray irradiation (1,5 Gy) on peripheral blood of bank voles (Myodes glareolus (Schreber, 1780)) captured within territories with background radiation level was conducted. Hematological indicators, characterizing the overall condition of performance of the body, were determined dynamically on the first and seventh days after exposure to detect both early changes and the rate of recovery processes. The patterns and features of the main components of leukocyte formula found in peripheral blood of irradiated animals are being discussed. Differences between irradiated and control mouse-like rodents are shown, using parameters of erythrocytes and leukocytes. The analysis of changes in the peripheral blood of irradiated bank voles indicates the high reserve capacity of the body, according to its ability to restore homeostasis.
Atomic physics. Constitution and properties of matter
Identifying the surface chemistry of diamond materials is increasingly important for device applications, especially quantum sensors. Oxygen-related termination species are widely used because they are naturally abundant, chemically stable, and compatible with stable nitrogen vacancy centres near the diamond surface. Diamond surfaces host a mixture of oxygen-related species, and the precise chemistry and relative coverage of different species can lead to dramatically different electronic properties, with direct consequences for near-surface quantum sensors. However, it is challenging to unambiguously identify the different groups or quantify the relative surface coverage. Here we show that a combination of x-ray absorption and photoelectron spectroscopies can be used to quantitatively identify the coverage of carbonyl functional groups on the $\{100\}$ diamond surface. Using this method we reveal an unexpectedly high fraction of carbonyl groups ( ${\gt}$ 9%) on a wide range of sample surfaces. Furthermore, through a combination of ab initio calculations and spectroscopic studies of engineered surfaces, we reveal unexpected complexities in the x-ray spectroscopy of oxygen terminated diamond surfaces. Of particular note, we find the binding energies of carbonyl-related groups on diamond differs significantly from other organic systems, likely resulting in previous misestimation of carbonyl fractions on diamond surfaces.
Atomic physics. Constitution and properties of matter, Materials of engineering and construction. Mechanics of materials
Shor's algorithm solves the integer factoring and discrete logarithm problems in polynomial time. Therefore, the evaluation of Shor's algorithm is essential for evaluating the security of currently used public-key cryptosystems because the integer factoring and discrete logarithm problems are crucial for the security of these cryptosystems. In this article, a new approximate quantum Fourier transform is proposed, and it is applied to Rines and Chuang's implementation. The proposed implementation requires one-third the number of <inline-formula><tex-math notation="LaTeX">$T$</tex-math></inline-formula> gates of the original. Moreover, it requires one-fourth of the <inline-formula><tex-math notation="LaTeX">$T$</tex-math></inline-formula>-depth of the original. Finally, a <inline-formula><tex-math notation="LaTeX">$T$</tex-math></inline-formula>-scheduling method for running the circuit with the smallest KQ (where K is the number of logical qubits and Q is the circuit depth) is presented.
Atomic physics. Constitution and properties of matter, Materials of engineering and construction. Mechanics of materials
As a result of the modernization of the DRG-05M dosimeter, a convenient device was obtained, which allows estimating the level of gamma- and X-ray radiation, beta-particles, and neutrons without changing the detector heads. Two devices were manufactured and a third one was prepared for metrological certification.
Atomic physics. Constitution and properties of matter
This article addresses the formulation for implementing a single source, single-destination shortest path algorithm on a quantum annealing computer. Three distinct approaches are presented. In all the three cases, the shortest path problem is formulated as a quadratic unconstrained binary optimization problem amenable to quantum annealing. The first implementation builds on existing quantum annealing solutions to the traveling salesman problem, and requires the anticipated maximum number of vertices on the solution path |P| to be provided as an input. For a graph with |V| vertices, |E| edges, and no self-loops, it encodes the problem instance using |V||P| qubits. The second implementation adapts the linear programming formulation of the shortest path problem, and encodes the problem instance using |E| qubits for directed graphs or 2|E| qubits for undirected graphs. The third implementation, designed exclusively for undirected graphs, encodes the problem in |E| + |V| qubits. Scaling factors for penalty terms, complexity of coupling matrix construction, and numerical estimates of the annealing time required to find the shortest path are made explicit in the article.
Atomic physics. Constitution and properties of matter, Materials of engineering and construction. Mechanics of materials
Ferroelectricity: General approach for designing new ferroelectric materials An innovative computational method could enable the design of new classes of ferroelectric materials. Ferroelectrics, whose spontaneous electric polarizations can be switched electrically, are useful for a range of applications, such as memory or sensing devices. However, relatively few naturally occurring materials are ferroelectric, and, while theoretical methods for designing new ferroelectrics are available, they are usually restricted to highly symmetric systems such as perovskite oxides. A team led by Hongjun Xiang from Fudan University have now developed a more general computational approach that can be applied to any system, and have used it to identify previously unrecognized classes of ferroelectrics. Such an approach could not only enable new ferroelectrics to be discovered, but it may also be suitable for designing multiferroic systems.
Materials of engineering and construction. Mechanics of materials, Atomic physics. Constitution and properties of matter