Quantum phase diffusion in a small underdamped Nb/AlO x /Nb junction (∼ 0.4 µm 2 ) is demonstrated in a wide temperature range of 25-140 mK where macroscopic quantum tunneling (MQT) is the dominant escape mechanism. We propose a two-step transition model to describe the switching process in which the escape rate out of the potential well and the transition rate from phase diffusion to the running state are considered. The transition rate extracted from the experimental switching current distribution follows the predicted Arrhenius law in the thermal regime but is greatly enhanced when MQT becomes dominant. PACS numbers: 74.50.+r, 85.25.Cp Classical and quantum diffusion of Brownian particles in titled periodic potential plays a fundamental role in the dynamical behavior of many systems in science and engineering [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. Examples include current biased Josephson junctions [1][2][3][4][5][6][7][8][9], colloidal particles in arrays of laser traps [10,11], cold atoms in optical lattice or Bose-Einstein condensates [12][13][14], and various biology-inspired systems known as Brownian motors (molecular motors or life engines), which receive considerable attention in physics [15] and chemistry [16]. Because of the design flexibility, manufacturability, and controllability Josephson junctions provide an excellent test bed for making quantitative comparison of experimental data with theoretical predictions and unraveling possible new physics in the tilted periodic potential systems.The dynamics of a current biased Josephson junction can be visualized as a fictitious phase particle of mass C moving in a tilted periodic potential U(ϕ) = −E J (iϕ + cos ϕ). Here, C is junction capacitance, i = I/I c is the junction's bias current normalized to its critical current, the phase particle's position ϕ is the gauge invariant phase difference across the junction, and E J = I c /2e is the Josephson coupling energy with e and being the electron charge and Planck's constant, respectively. Previous experiments using Josephson junctions have identified three distinctive dynamical states, as shown schematically in Fig. 1. In the first state, the phase particle is trapped in one of the metastable potential wells and undergoes small oscillation around the bottom of the well with plasma frequency ω p . Because of thermal and/or quantum fluctuations the particle has a finite rate Γ 1 escaping from the trapped state. The escape rate becomes significant when the barrier height ∆U is not much greater than k B T or ω p , where k B is the Boltzmann constant and T denotes the temperature, respectively. After the particle escapes from the initial well, depending on the energy gain δU = Φ 0 I (Φ 0 being the flux quantum) and the loss E D due to damping (cf. Fig. 1), it could enter either the second dynamical state called phase diffusion (PD) or the final running state. In the former case as the bias current I is increased further the particle will eventually make a transition, characterized by a rat...

Here we report a breakthrough in the fabrication of a long lifetime transmon qubit. We use tantalum films as the base superconductor. By using a dry etching process, we obtained transmon qubits with a best T1 lifetime of 503 μs. As a comparison, we also fabricated transmon qubits with other popular materials, including niobium and aluminum, under the same design and fabrication processes. After characterizing their coherence properties, we found that qubits prepared with tantalum films have the best performance. Since the dry etching process is stable and highly anisotropic, it is much more suitable for fabricating complex scalable quantum circuits, when compared to wet etching. As a result, the current breakthrough indicates that the dry etching process of tantalum film is a promising approach to fabricate medium- or large-scale superconducting quantum circuits with a much longer lifetime, meeting the requirements for building practical quantum computers.

Lidocaine has been reported to induce apoptosis on rabbit corneal endothelial cells. However, the apoptotic effect and exact mechanism involved in cytotoxicity of lidocaine are not well-established in human corneal endothelial (HCE) cells. In this study, we investigated the apoptosis-inducing effect of lidocaine on HCE cells in vitro. After HCE cells were treated with lidocaine at concentrations of 0.15625-10.0 g/l, the morphology and ultrastructure of the cells were observed by inverted light microscope and transmission electron microscope (TEM). Cell viability was measured by MTT assay, and the apoptotic ratio was evaluated with flow cytometry and fluorescent microscopic counting after FITC-Annexin V/PI and AO/EB staining. DNA fragmentation was detected by electrophoresis, and the activation of caspases was evaluated by ELISA. In addition, changes in mitochondrial membrane potential were determined by JC-1 staining. Results suggest that lidocaine above 1.25 g/l reduced cellular viability and triggered apoptosis in HCE cells in a time-and dose-dependent manner. Diminishment of DΨm and the activation of caspases indicate that lidocaine-induced apoptosis was caspase dependent and may be related to mitochondrial pathway.Human corneal endothelium (HCE), a functional monolayer forming the demarcation between cornea and anterior chamber, plays pivotal roles in maintaining corneal transparency by regulating corneal stromal water content [1]. Notwithstanding the evidence of proliferation when deprived of their nature environment, HCE cells are trapped in the G1 phase of the cell cycle and have a limited, if not restricted, proliferative capacity in vivo [2,3], accompanied by an annual attrition rate of 0.3-0.6% in cell density during adulthood [4].In addition to ageing, excessive HCE cell loss may result from accidental injuries, surgical trauma and diseases [5][6][7] which consequently impair the physiology of cornea. Due to the inability of HCE to be repaired through cell number increase, wound healing can only be achieved by enlargement and migration of the neighbouring cells. However, if the decline of cell density transcends a threshold, the integrity of the corneal endothelium will be compromised, resulting in painful corneal oedema and ultimately loss of visual acuity. Recently, increased evidence has revealed corneal endothelium damage to be associated with abused administration of topical anaesthetics [8][9][10].Lidocaine is one of the most frequently used topical anaesthetic agents in ophthalmic surgeries for its inherent potency, rapid onset, tissue penetration and efficiency [11]. It can result in corneal thickening, opacification and significant corneal endothelial cell loss when applied intracamerally [12]. In addition, administration of lidocaine has been shown to cause an increase in apoptotic cells in corneal endothelium in rabbit models [13]. However, the side effects of lidocaine on HCE cells and their mechanism remain unknown. In this study, we aimed to investigate the apoptosis-inducing e...

Articles you may be interested inResistive switching characteristics of integrated polycrystalline hafnium oxide based one transistor and one resistor devices fabricated by atomic vapor deposition methods J. Vac. Sci. Technol. B 33, 052204 (2015) Atomic Layer Deposition (ALD) is a promising technique for growing ultrathin, pristine dielectrics on metal substrates, which is essential to many electronic devices. Tunnel junctions are an excellent example which require a leak-free, ultrathin dielectric tunnel barrier of typical thickness around 1 nm between two metal electrodes. A challenge in the development of ultrathin dielectric tunnel barriers using ALD is controlling the nucleation of dielectrics on metals with minimal formation of native oxides at the metal surface for high-quality interfaces between the tunnel barrier and metal electrodes. This poses a critical need for integrating ALD with ultra-high vacuum (UHV) physical vapor deposition. In order to address these challenges, a viscous-flow ALD chamber was designed and interfaced to an UHV magnetron sputtering chamber via a load lock. A sample transportation system was implemented for in situ sample transfer between the ALD, load lock, and sputtering chambers. Using this integrated ALD-UHV sputtering system, superconductor-insulator-superconductor (SIS) Nb-Al/Al 2 O 2 /Nb Josephson tunnel junctions were fabricated with tunnel barriers of thickness varied from sub-nm to ∼1 nm. The suitability of using an Al wetting layer for initiation of the ALD Al 2 O 3 tunnel barrier was investigated with ellipsometry, atomic force microscopy, and electrical transport measurements. With optimized processing conditions, leak-free SIS tunnel junctions were obtained, demonstrating the viability of this integrated ALD-UHV sputtering system for the fabrication of tunnel junctions and devices comprised of metal-dielectric-metal multilayers. © 2014 AIP Publishing LLC. [http://dx