104 research outputs found
Treatment of DomesticWastewaterwith Simultaneous Electricity Generation in Microbial Fuel Cell under Continuous Operation
In order to apply microbial fuel cell (MFC) process more practically in wastewater treatment, both power generation and removal of chemical oxygen demand (COD) were examined in an air-cathode MFC fed with domestic wastewater under continuous operation.
At a hydraulic retention time (HRT) of 2.0 h, the air-cathode MFC was able to generate electricity from domestic wastewater with a maximum power density of P = 103 2 mWm–2 (5772 mW m–3) and an average Coulomb efficiency (CE) of 18.4%; meanwhile,
to achieve an average COD removal up to 71 %. Increasing HRT from 2h to 10–30 h was found to be more effective for COD removal, however, instability in voltage output was also observed. An increased power generation of 1734mW m–2 (9648 mW m–3) was obtained with the aid of NaCl addition at a mass fraction of w = 2.4 %, because of an elevated conductivity of the solution with accord internal resistance of 227 0
Non-Markovian entanglement dynamics in coupled superconducting qubit systems
We theoretically analyze the entanglement generation and dynamics by coupled
Josephson junction qubits. Considering a current-biased Josephson junction
(CBJJ), we generate maximally entangled states. In particular, the entanglement
dynamics is considered as a function of the decoherence parameters, such as the
temperature, the ratio between the reservoir cutoff
frequency and the system oscillator frequency , % between
the characteristic frequency of the %quantum system of interest, and
the cut-off frequency of %Ohmic reservoir and the energy levels
split of the superconducting circuits in the non-Markovian master equation. We
analyzed the entanglement sudden death (ESD) and entanglement sudden birth
(ESB) by the non-Markovian master equation. Furthermore, we find that the
larger the ratio and the thermal energy , the shorter the
decoherence. In this superconducting qubit system we find that the entanglement
can be controlled and the ESD time can be prolonged by adjusting the
temperature and the superconducting phases which split the energy
levels.Comment: 13 pages, 3 figure
Robust stationary entanglement of two coupled qubits in independent environments
The dissipative dynamics of two interacting qubits coupled to independent
reservoirs at nonzero temperatures is investigated, paying special attention to
the entanglement evolution. The counter-rotating terms in the qubit-qubit
interaction give rise to stationary entanglement, traceable back to the ground
state structure. The robustness of this entanglement against thermal noise is
thoroughly analyzed, establishing that it can be detected at reasonable
experimental temperatures. Some effects linked to a possible reservoir
asymmetry are brought to light.Comment: 8 pages, 6 figures; version accepted for publication on Eur. Phys. J.
Controlled-NOT logic gate for phase qubits based on conditional spectroscopy
A controlled-NOT logic gate based on conditional spectroscopy has been
demonstrated recently for a pair of superconducting flux qubits [Plantenberg et
al., Nature 447, 836 (2007)]. Here we study the fidelity of this type of gate
applied to a phase qubit coupled to a resonator (or a pair of capacitively
coupled phase qubits). Our results show that an intrinsic fidelity of more than
99% is achievable in 45ns.Comment: 5 pages, 5 figures, To appear in Quantum Inf. Pro
Quantum information processing with superconducting qubits in a microwave field
We investigate the quantum dynamics of a Cooper-pair box with a
superconducting loop in the presence of a nonclassical microwave field. We
demonstrate the existence of Rabi oscillations for both single- and
multi-photon processes and, moreover, we propose a new quantum computing scheme
(including one-bit and conditional two-bit gates) based on Josephson qubits
coupled through microwaves.Comment: 7 pages, 1 figur
Fast geometric gate operation of superconducting charge qubits in circuit QED
A scheme for coupling superconducting charge qubits via a one-dimensional
superconducting transmission line resonator is proposed. The qubits are working
at their optimal points, where they are immune to the charge noise and possess
long decoherence time. Analysis on the dynamical time evolution of the
interaction is presented, which is shown to be insensitive to the initial state
of the resonator field. This scheme enables fast gate operation and is readily
scalable to multiqubit scenario
Dispersive Manipulation of Paired Superconducting Qubits
We combine the ideas of qubit encoding and dispersive dynamics to enable
robust and easy quantum information processing (QIP) on paired superconducting
charge boxes sharing a common bias lead. We establish a decoherence free
subspace on these and introduce universal gates by dispersive interaction with
a LC resonator and inductive couplings between the encoded qubits. These gates
preserve the code space and only require the established local symmetry and the
control of the voltage bias.Comment: 5 pages, incl. 1 figur
Life after charge noise: recent results with transmon qubits
We review the main theoretical and experimental results for the transmon, a
superconducting charge qubit derived from the Cooper pair box. The increased
ratio of the Josephson to charging energy results in an exponential suppression
of the transmon's sensitivity to 1/f charge noise. This has been observed
experimentally and yields homogeneous broadening, negligible pure dephasing,
and long coherence times of up to 3 microseconds. Anharmonicity of the energy
spectrum is required for qubit operation, and has been proven to be sufficient
in transmon devices. Transmons have been implemented in a wide array of
experiments, demonstrating consistent and reproducible results in very good
agreement with theory.Comment: 6 pages, 4 figures. Review article, accepted for publication in
Quantum Inf. Pro
Time-Dependent Partition-Free Approach in Resonant Tunneling Systems
An extended Keldysh formalism, well suited to properly take into account the
initial correlations, is used in order to deal with the time-dependent current
response of a resonant tunneling system. We use a \textit{partition-free}
approach by Cini in which the whole system is in equilibrium before an external
bias is switched on. No fictitious partitions are used. Besides the
steady-state responses one can also calculate physical dynamical responses. In
the noninteracting case we clarify under what circumstances a steady-state
current develops and compare our result with the one obtained in the
partitioned scheme. We prove a Theorem of asymptotic Equivalence between the
two schemes for arbitrary time-dependent disturbances. We also show that the
steady-state current is independent of the history of the external perturbation
(Memory Loss Theorem). In the so called wide-band limit an analytic result for
the time-dependent current is obtained. In the interacting case we propose an
exact non-equilibrium Green function approach based on Time Dependent Density
Functional Theory. The equations are no more difficult than an ordinary Mean
Field treatment. We show how the scattering-state scheme by Lang follows from
our formulation. An exact formula for the steady-state current of an arbitrary
interacting resonant tunneling system is obtained. As an example the
time-dependent current response is calculated in the Random Phase
Approximation.Comment: final version, 18 pages, 9 figure
Clauser-Horne inequality for electron counting statistics in multiterminal mesoscopic conductors
In this paper we derive the Clauser-Horne (CH) inequality for the full
electron counting statistics in a mesoscopic multiterminal conductor and we
discuss its properties. We first consider the idealized situation in which a
flux of entangled electrons is generated by an entangler. Given a certain
average number of incoming entangled electrons, the CH inequality can be
evaluated for different numbers of transmitted particles. Strong violations
occur when the number of transmitted charges on the two terminals is the same
(), whereas no violation is found for . We then consider
two actual setups that can be realized experimentally. The first one consists
of a three terminal normal beam splitter and the second one of a hybrid
superconducting structure. Interestingly, we find that the CH inequality is
violated for the three terminal normal device. The maximum violation scales as
1/M and for the entangler and normal beam splitter, respectively, 2
being the average number of injected electrons. As expected, we find full
violation of the CH inequality in the case of the superconducting system.Comment: 26 pages, 9 figures. Ref. adde
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