All single-valent oxide spinels are insulators. The relatively small activation energy in the temperature dependence of resistivity in vanadate spinels led to the speculation that the spinels are near the crossover from localized to itinerant electronic behavior, and the crossover could be achieved under pressure. We have performed a number of experiments and calculations aimed at obtaining information regarding structural changes under high pressure for the whole series of vanadate spinels, as well as transport and magnetic properties under pressure for $\mathrm{Mg}{\mathrm{V}}_{2}{\mathrm{O}}_{4}$. We have also studied the crystal structure under pressure of wide-gap insulators $A\mathrm{C}{\mathrm{r}}_{2}{\mathrm{O}}_{4}$ ($A=\phantom{\rule{0.16em}{0ex}}\mathrm{Mg}$, Mn, Fe, Zn) for comparison. Moreover, the relationship between the bulk modulus and the cell volume of $A{\mathrm{V}}_{2}{\mathrm{O}}_{4}$ ($A=\phantom{\rule{0.16em}{0ex}}\mathrm{Mg}$, Mn, Fe, Co, Zn) has been simulated by a density functional theory calculation. The proximity of $A{\mathrm{V}}_{2}{\mathrm{O}}_{4}$ spinels to the electronic state crossover under high pressure has been tested by three criteria: (1) a predicted critical V-V bond length, (2) the observation of a sign change in the pressure dependence of N\'eel temperature, and (3) measurement of a reduced bulk modulus. The obtained results indicate that, although the crossover from localized to itinerant \ensuremath{\pi} bonding $\text{V-}3d$ electrons in the $A{\mathrm{V}}_{2}{\mathrm{O}}_{4}$ spinels is approached by reducing under pressure the V-V separation $R$, the critical separation ${R}_{\mathrm{c}}$ is not reached by 20 GPa in $\mathrm{Co}{\mathrm{V}}_{2}{\mathrm{O}}_{4}$, which has the smallest V-V separation in the $A{\mathrm{V}}_{2}{\mathrm{O}}_{4}$ ($A=\phantom{\rule{0.16em}{0ex}}\mathrm{Mg}$, Mn, Fe, Co, Zn) spinels.
The increasing control complexity of Noisy Intermediate-Scale Quantum (NISQ) systems underlines the necessity of integrating quantum hardware with quantum software. While mapping heterogeneous quantum-classical computing (HQCC) algorithms to NISQ hardware for execution, we observed a few dissatisfactions in quantum programming languages (QPLs), including difficult mapping to hardware, limited expressiveness, and counter-intuitive code. In addition, noisy qubits require repeatedly performed quantum experiments, which explicitly operate low-level configurations, such as pulses and timing of operations. This requirement is beyond the scope or capability of most existing QPLs. We summarize three execution models to depict the quantum-classical interaction of existing QPLs. Based on the refined HQCC model, we propose the Quingo framework to integrate and manage quantum-classical software and hardware to provide the programmability over HQCC applications and map them to NISQ hardware. We propose a six-phase quantum program life-cycle model matching the refined HQCC model, which is implemented by a runtime system. We also propose the Quingo programming language, an external domain-specific language highlighting timer-based timing control and opaque operation definition, which can be used to describe quantum experiments. We believe the Quingo framework could contribute to the clarification of key techniques in the design of future HQCC systems.
The Google's PageRank algorithm is one of the most famous algorithms in data mining. A quantum version of this algorithm has been proposed in 2012. It is a meaningful step towards the quantum search engine but it can not search solutions. In this paper, we integrate a special operator of quantum search into the quantum PageRank algorithm to make a new quantum algorithm. We called it the Search Rank algorithm. This new algorithm is able to search solutions and rank results according to their importance at the same time. It is the first algorithm possessing this ability as far as we know. And it outperforms all classical algorithms when searching an unsorted database.
The wave–particle duality relation derived by Englert sets an upper bound of the extractable information from wave and particle properties in a two-path interferometer. Surprisingly, previous studies demonstrated that the introduction of a quantum beamsplitter in the interferometer could break the limitation of this upper bound, due to interference between wave and particle states. Along the other line, a lot of efforts have been made to generalize this relation from the two-path setup to the N -path case. Thus, it is an interesting question that whether a quantum N -path beamsplitter can break the limitation as well. This paper systemically studies the model of a quantum N -path beamsplitter, and finds that the generalized wave–particle duality relation between interference visibility and path distinguishability is also broken in certain situations. We further study the maximal extractable information’s reliance on the interference between wave and particle properties, and derive a quantitative description. We then propose an experimental methodology to verify the break of the limitation. Our work reflects the effect of quantum superposition on wave–particle duality, and exhibits a new aspect of the relation between visibility and path distinguishability in N -path interference. Moreover, it implies the observer’s influence on wave–particle duality.
We demonstrate a bias-free true random number generator (TRNG) based on single photon detection using superconducting nanowire single photon detectors (SNSPDs). By comparing the photon detection signals of two consecutive laser pulses and extracting the random bits by the von Neumann correction method, we achieved a random number generation efficiency of 25% (a generation rate of 3.75 Mbit s−1 at a system clock rate of 15 MHz). Using a multi-channel superconducting nanowire single photon detector system with controllable pulse signal amplitudes, we detected the single photons with photon number resolution and positional sensitivity, which could further increase the random number generation efficiency. In a three-channel SNSPD system, the random number bit generation efficiency was improved to 75%, corresponding to a generation rate of 7.5 Mbit s−1 with a 10 MHz system clock rate. All of the generated random numbers successfully passed the statistical test suite.
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