Scalable technologies to characterize the performance of quantum devices are crucial to creating large quantum networks and quantum processing units. Chief among the resources of quantum information processing is entanglement. Here we describe the full temporal and spatial characterization of polarization-entangled photons produced by Spontaneous Parametric Down Conversions using an intensified high-speed optical camera, Tpx3Cam. This novel technique allows for precise determination of Bell inequality parameters with minimal technical overhead, as well as novel characterization methods of the spatial distribution of entangled quantum information. This could lead to multiple applications in Quantum Information Science, opening new perspectives for the scalability of quantum experiments. arXiv:1808.06720v2 [quant-ph] 13 Sep 2018 Recent developments have shown that spatial characterization of entangled states with single-photon sensitive cameras provides access to a myriad of new possibilities, such as imaging high-dimensional entanglement [8], generalized Bell inequalities [9] and the study of Einstein-Podolsky-Rosen non-localities [10, 11]. However, these measurements used resource-intensive methods, such as sequential scanning or multiple standalone detectors.Early studies of entanglement with modern imagers used an electron-multiplying CCD (EM-CCD) camera with an effective area of 201 × 201 pixels and frame readout-rate of 5Hz [8].Albeit the EMCCD quantum efficiency was up to 90%, prolonged exposure time of about 1ms, requires this device to operate at very small photon-rates to avoid multiple photons in the same frame. Furthermore, to achieve single-photon level sensitivity the EMCCD camera operated at a low temperature of −85 o C.Further progression on quantum imaging with cameras was achieved using intensified CMOS and CCD cameras [12][13][14][15][16][17]. Flexible readout architectures allow kHz continuous framing rates in CMOS cameras. Additionally, nano-second scale time resolution for single photons can be achieved by gating image intensifiers. For example, an intensified sCMOS camera was used to observe Hong-Ou-Mandel interference [18], where the photons were collected on
The development of MnO 2 as a cathode for aqueous zinc-ion batteries (AZIBs) is severely limited by the low intrinsic electrical conductivity and unstable crystal structure. Herein, a multifunctional modification strategy is proposed to construct N-doped KMn 8 O 16 with abundant oxygen vacancy and large specific surface area (named as N-KMO) through a facile one-step hydrothermal approach. The synergetic effects of N-doping, oxygen vacancy, and porous structure in N-KMO can effectively suppress the dissolution of manganese ions, and promote ion diffusion and electron conduction. As a result, the N-KMO cathode exhibits dramatically improved stability and reaction kinetics, superior to the pristine MnO 2 and MnO 2 with only oxygen vacancy. Remarkably, the N-KMO cathode delivers a high reversible capacity of 262 mAh g −1 after 2500 cycles at 1 A g −1 with a capacity retention of 91%. Simultaneously, the highest specific capacity can reach 298 mAh g −1 at 0.1 A g −1 . Theoretical calculations reveal that the oxygen vacancy and N-doping can improve the electrical conductivity of MnO 2 and thus account for the outstanding rate performance. Moreover, ex situ characterizations indicate that the energy storage mechanism of the N-KMO cathode is mainly a H + and Zn 2+ co-insertion/extraction process.
We explore the quantum metrology in an optical molecular system coupled to two environments with different temperatures, using a quantum master equation beyond secular approximation. We discover that the steady-state coherence originating from and sustained by the nonequilibrium condition can enhance quantum metrology. We also study the quantitative measures of the nonequilibrium condition in terms of the curl flux, heat current and entropy production at the steady state. They are found to grow with temperature difference. However, an apparent paradox arises considering the contrary behaviors of the steady-state coherence and the nonequilibrium measures in relation to the inter-cavity coupling strength. This paradox is resolved by decomposing the heat current into a population part and a coherence part. Only the latter, coherence heat current, is tightly connected to the steady-state coherence and behaves similarly with respect to the inter-cavity coupling strength. Interestingly, the coherence heat current flows from the low-temperature reservoir to the high-temperature reservoir, opposite to the direction of the population heat current. Our work offers a viable way to enhance quantum metrology for open quantum systems through steady-state coherence sustained by the nonequilibrium condition, which can be controlled and manipulated to maximize its utility. The potential applications go beyond quantum metrology and extend to areas such as device designing, quantum computation and quantum technology in general.
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