An important unresolved question in plasma physics concerns the effect of strong electron emission on plasma-surface interactions. Previous papers reported solutions with negative and positive ...floating potentials relative to the plasma edge. The two models give very different predictions for particle and energy balance. Here we show that the positive potential state is the only possible equilibrium in general. Even if a negative floating potential existed at t=0, the ionization collisions near the surface will force a transition to the positive floating potential state. This transition is demonstrated with a new simulation code.
Quantum computers have the potential to solve certain problems faster than classical computers. To exploit their power, it is necessary to perform interqubit operations and generate entangled states. ...Spin qubits are a promising candidate for implementing a quantum processor because of their potential for scalability and miniaturization. However, their weak interactions with the environment, which lead to their long coherence times, make interqubit operations challenging. We performed a controlled two-qubit operation between singlet-triplet qubits using a dynamically decoupled sequence that maintains the two-qubit coupling while decoupling each qubit from its fluctuating environment. Using state tomography, we measured the full density matrix of the system and determined the concurrence and the fidelity of the generated state, providing proof of entanglement.
Two level systems that can be reliably controlled and measured hold promise as qubits both for metrology and for quantum information science. Since a fluctuating environment limits the performance of ...qubits in both capacities, understanding environmental coupling and dynamics is key to improving qubit performance. We show measurements of the level splitting and dephasing due to the voltage noise of a GaAs singlet-triplet qubit during exchange oscillations. Unexpectedly, the voltage fluctuations are non-Markovian even at high frequencies and exhibit a strong temperature dependence. This finding has impacts beyond singlet-triplet qubits since nearly all solid state qubits suffer from some kind of charge noise. The magnitude of the fluctuations allows the qubit to be used as a charge sensor with a sensitivity of 2 × 10(-8)e/sqrtHz, 2 orders of magnitude better than a quantum-limited rf single electron transistor. Based on these measurements, we provide recommendations for improving qubit coherence, allowing for higher fidelity operations and improved charge sensitivity.
Unwanted interaction between a quantum system and its fluctuating environment leads to decoherence and is the primary obstacle to establishing a scalable quantum information processing architecture. ...Strategies such as environmental and materials engineering, quantum error correction and dynamical decoupling can mitigate decoherence, but generally increase experimental complexity. Here we improve coherence in a qubit using real-time Hamiltonian parameter estimation. Using a rapidly converging Bayesian approach, we precisely measure the splitting in a singlet-triplet spin qubit faster than the surrounding nuclear bath fluctuates. We continuously adjust qubit control parameters based on this information, thereby improving the inhomogenously broadened coherence time (T2*) from tens of nanoseconds to >2 μs. Because the technique demonstrated here is compatible with arbitrary qubit operations, it is a natural complement to quantum error correction and can be used to improve the performance of a wide variety of qubits in both meteorological and quantum information processing applications.
High-temperature vacuum impregnation of micro- and ultradispersed diamond powders (MDDP and UDDP) of the ASM 50/40, ASM 14/10, ASM 10/7, ASM 5/3, and ASM 1/0 grades, metal powders Ti, V, Nb, Ta, Cr, ...Mo, W, Fe, Co, and Ni, as well and also their mixtures with some copper-based alloys was studied. It was determined that ASM 50/40 and ASM 14/10 diamond powders can be impregnated with an adhesive-active copper-based alloy Cu–20.3 Ti–4.6 Sn–2.8 Ni–0.15 Si–0.1 B. Diamond powders of ASM 10/7, ASM 5/3, and ASM 1/0 were not impregnated at all with such an alloy, as well as with nonadhesive-active alloys Cu–15.0 Sn, Cu–15.0 Ge, Cu–18.8 Ga. Metal powders Ti, V, Nb, Cr, Fe, Co, and Ni were well impregnated, and metal powders Ta, Mo, W were not impregnated with alloys Cu–15.0 Sn, Cu–15.0 Ge, Cu–18.8 Ga (except for the adhesive-active alloy). A thin oxide layer was always observed on the surface of metal powder particles. Metal powders of the first group (Ti, V, Nb, Cr, Fe, Co, Ni) are unstable and easily reduced by vacuum heating, and therefore are well wetted and impregnated with the studied alloys. In the second group (Ta, Mo, W), chemically resistant surface oxides interfered with the processes of wetting– impregnation. Due to the process of contact-reaction impregnation of MDDP or UDDP mixtures with Ta, Mo, and W metal powders, a non-porous high-strength composite material was obtained, in which the diamond grains are securely fastened. Oxides of such metals were partially reduced by diamond carbon, and the grain surfaces of diamond powders were metalized (covered with a thin layer of metal) due to partial evaporation of oxides, their deposition on the surface of diamond grains, and reduction to pure juvenile metals. Thus, both components of the mixture were very well wetted and impregnated with the investigated melts. The use of an adhesive-active alloy or a mixture of MDDP and UDDP powders with Ti, V, Nb, Cr, Fe, Co, Ni is undesirable due to the chemical interaction of Ti, V, Nb, Cr with the material of the mold used for the tool manufacture or diamond graphitization in the presence of process catalysts: Fe, Co, Ni.
The fractional quantum Hall effect, where plateaus in the Hall resistance at values of h/nue2 coexist with zeros in the longitudinal resistance, results from electron correlations in two dimensions ...under a strong magnetic field. (Here h is Planck's constant, nu the filling factor and e the electron charge.) Current flows along the sample edges and is carried by charged excitations (quasiparticles) whose charge is a fraction of the electron charge. Although earlier research concentrated on odd denominator fractional values of nu, the observation of the even denominator nu = 5/2 state sparked much interest. This state is conjectured to be characterized by quasiparticles of charge e/4, whose statistics are 'non-abelian'-in other words, interchanging two quasiparticles may modify the state of the system into a different one, rather than just adding a phase as is the case for fermions or bosons. As such, these quasiparticles may be useful for the construction of a topological quantum computer. Here we report data on shot noise generated by partitioning edge currents in the nu = 5/2 state, consistent with the charge of the quasiparticle being e/4, and inconsistent with other possible values, such as e/2 and e. Although this finding does not prove the non-abelian nature of the nu = 5/2 state, it is the first step towards a full understanding of these new fractional charges.
Electron pairing is a rare phenomenon appearing only in a few unique physical systems; for example, superconductors and Kondo-correlated quantum dots. Here, we report on an unexpected electron ...pairing in the integer quantum Hall effect regime. The pairing takes place within an interfering edge channel in an electronic Fabry-Perot interferometer at a wide range of bulk filling factors, between 2 and 5. We report on three main observations: high-visibility Aharonov-Bohm conductance oscillations with magnetic flux periodicity equal to half the magnetic flux quantum; an interfering quasiparticle charge equal to twice the elementary electron charge as revealed by quantum shot noise measurements, and full dephasing of the pairs' interference by induced dephasing of the adjacent inner edge channel-a manifestation of inter-channel entanglement. Although this pairing phenomenon clearly results from inter-channel interaction, the exact mechanism that leads to electron-electron attraction within a single edge channel is not clear. We believe that substantial efforts are needed in order to clarify these intriguing and unexpected findings.
Summary
In recent years, percutaneous radiofrequency ablation (RFA) has been developed as a new tool in the treatment of non‐small‐cell lung cancer (NSCLC) in non‐surgical patients. There is growing ...evidence that RFA‐mediated necrosis can modulate host immune responses. Here we analysed serum inflammatory factors as well as immunosuppressive cells in the peripheral blood to discover possible prognostic indicators. Peripheral blood and serum samples were collected before RFA and within 3 months after the treatment in a total of 12 patients. Inflammatory cytokines and growth factors were measured in serum by the Bio‐Plex assay. Myeloid‐derived suppressor cells (MDSCs) and regulatory T cells (Tregs) were evaluated in the peripheral blood via flow cytometry. In patients developing local or lymphogenic tumour relapse (n = 4), we found an early significant increase in the concentration of tumour necrosis factor (TNF)‐α as well as chemokine (C‐C motif) ligand (CCL)‐2 and CCL‐4 compared to patients without relapse (n = 4) and healthy donors (n = 5). These changes were associated with an elevated activity of circulating MDSC indicated by an increased nitric oxide (NO) production in these cells. Elevated serum levels of TNF‐α, CCL‐2 and CCL‐4 associated with an increased NO production in circulating MDSCs might be an early indicator of the incomplete RFA and subsequently a potential tumour relapse in NSCLC.
Studies of electronic interferometers, based on edge-channel transport in the quantum Hall effect regime, have been stimulated by the search for evidence of abelian and non-abelian anyonic statistics ...of fractional charges. In particular, the electronic Fabry-Pérot interferometer has been found to be Coulomb dominated, thus masking coherent Aharonov-Bohm interference patterns: the flux trapped within the interferometer remains unchanged as the applied magnetic field is varied, barring unobservable modulations of the interference area. Here we report on conductance measurements indicative of the interferometer's area 'breathing' with the variation of the magnetic field, associated with observable (a fraction of a flux quantum) variations of the trapped flux. This is the result of partial (controlled) screening of Coulomb interactions. Our results introduce a novel experimental tool for probing anyonic statistics.
Quantum critical systems derive their finite-temperature properties from the influence of a zero-temperature quantum phase transition. The paradigm is essential for understanding unconventional ...high-Tc superconductors and the non-Fermi liquid properties of heavy fermion compounds. However, the microscopic origins of quantum phase transitions in complex materials are often debated. Here we demonstrate experimentally, with support from numerical renormalization group calculations, a universal crossover from quantum critical non-Fermi liquid behaviour to distinct Fermi liquid ground states in a highly controllable quantum dot device. Our device realizes the non-Fermi liquid two-channel Kondo state, based on a spin-1/2 impurity exchange-coupled equally to two independent electronic reservoirs. On detuning the exchange couplings we observe the Fermi liquid scale T*, at energies below which the spin is screened conventionally by the more strongly coupled channel. We extract a quadratic dependence of T* on gate voltage close to criticality, and validate an asymptotically exact description of the universal crossover between strongly correlated non-Fermi liquid and Fermi liquid states.
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