Identification of Coulomb blockade and macroscopic quantum tunneling by noise

The effects of Macroscopic Quantum Tunneling (MQT) and Coulomb Blockade (CB) in Josephson junctions are of considerable significance both for the manifestations of quantum mechanics on the macroscopic scale and potential technological applications. These two complementary effects are shown to be clearly distinguishable from the associated noise spectra. The current noise is determined exactly and a rather sharp crossover between flux noise in the MQT and charge noise in the CB regions is found as the applied voltage is changed. Related results hold for the voltage noise in current-biased junctions.Comment: 6 pages, 3 figures, epl.cls include

T-Bar clasp-retained removable partial denture as an alternative to implant-based prosthetic treatment

This article reports the case of a 55-year-old female patient who presented with unsatisfactory temporary crowns in the right mandibular premolars and molars, and a premolar-to-molar fixed partial denture in the left side. The clinical and radiographic examinations revealed a fracture of the left first premolar that was a retainer of the fixed partial denture and required extraction. Initially, the acrylic resin crowns were replaced by new ones, and a provisional RPD was made using acrylic resin and orthodontic wire clasps to resolve the problem arising from the loss of the fixed partial denture. Considering the patient's high esthetic demands, the treatment options for the definitive prosthetic treatment were discussed with her and rehabilitation with implant-supported dentures was proposed because the clinical conditions of the residual alveolar ridge were suitable for implant installation, and the patient's general health was excellent. However, the patient did not agree because she knew of a failed case of implant-retained denture in a diabetic individual and was concerned. The patient was fully informed that implant installation was the best indication for her case, but the arguments were not sufficient to change her decision. The treatment possibilities were presented and the patient opted for a clasp-retained removable partial denture (RPD) associated with the placement of crowns in the pillar teeth. The temporary RPD was replaced by the definitive RPD constructed subsequently. Although RPD was not the first choice, satisfactory esthetic and functional outcomes were achieved, overcaming the patient's expectations. This case report illustrates that the dentist must be prepared to deal with situations where, for reasons that cannot be managed, the patient does not accept the treatment considered as the most indicated for his/her case. Alternatives must be proposed and the functional and esthetic requirements must be fulfilled in the best possible manner.Este artigo relata o caso de uma paciente de 55 anos que apresentava no arco mandibular coroas provisórias insatisfatórias nos pré-molares do lado direito e uma prótese parcial fixa de molar a pré-molar no lado esquerdo. Os exames clínico e radiográfico revelaram uma fratura do primeiro pré-molar esquerdo que era um retentor da prótese parcial fixa e teve a extração indicada. Inicialmente, as coroas provisórias foram substituídas por novas e uma prótese parcial removível provisória foi confeccionada com resina acrílica e grampos de fio ortodôntico a fim resolver os problemas relacionados à perda da prótese parcial fixa. Considerando a forte demanda estética da paciente, foram discutidas as opções de tratamento protético definitivo. Foi proposta a reabilitação com prótese implanto-suportada uma vez que as condições clínicas do rebordo alveolar se apresentavam adequadas para instalação de implantes e a saúde geral da paciente era excelente. Entretanto, a paciente não concordou com o tratamento proposto, alegando saber de um caso clínico em que houve insucesso na reabilitação por prótese implanto-suportada em um paciente diabético. Ela foi inteiramente informada de que a colocação de implantes era a melhor indicação para seu caso, mas os argumentos não foram suficientes para mudar sua decisão. As possibilidades de tratamento foram apresentadas e a paciente optou por uma prótese parcial removível (PPR) retida a grampos associada com coroas nos dentes pilares. Na seqüência, a PPR provisória foi substituída por uma PPR definitiva. Embora a PPR não tivesse sido a primeira escolha, foram obtidos resultados estéticos e funcionais satisfatórios, superando as expectativas da paciente. Este relato de caso ilustra que o dentista deve estar preparado para enfrentar situações em que, por razões que não possam ser administradas, o paciente não aceite o tratamento considerado mais indicado para seu caso. Alternativas devem ser propostas e as exigências estéticas e funcionais devem ser contempladas da melhor maneira possível

Quantum nondemolition-like, fast measurement scheme for a superconducting qubit

We present a measurement protocol for a flux qubit coupled to a dc-Superconducting QUantum Interference Device (SQUID), representative of any two-state system with a controllable coupling to an harmonic oscillator quadrature, which consists of two steps. First, the qubit state is imprinted onto the SQUID via a very short and strong interaction. We show that at the end of this step the qubit dephases completely, although the perturbation of the measured qubit observable during this step is weak. In the second step, information about the qubit is extracted by measuring the SQUID. This step can have arbitrarily long duration, since it no longer induces qubit errors.Comment: published version, minor correction

Phase-Charge Duality of a Josephson junction in a fluctuating electromagnetic environment

We have measured the current-voltage characteristics of a single Josephson junction placed in a high impedance environment. The transfer of Cooper pairs through the junction is governed by overdamped quasicharge dynamics, leading to Coulomb blockade and Bloch oscillations. Exact duality exists to the standard overdamped phase dynamics of a Josephson junction, resulting in a dual shape of the current-voltage characteristic, with current and voltage changing roles. We demonstrate this duality with experiments which allow for a quantitative comparison with a theory that includes the effect of fluctuations due to finite temperature of the electromagnetic environment

Crossover from weak to strong coupling regime in dispersive circuit QED

We study the decoherence of a superconducting qubit due to the dispersive coupling to a damped harmonic oscillator. We go beyond the weak qubit-oscillator coupling, which we associate with a phase Purcell effect, and enter into a strong coupling regime, with qualitatively different behavior of the dephasing rate. We identify and give a physicaly intuitive discussion of both decoherence mechanisms. Our results can be applied, with small adaptations, to a large variety of other physical systems, e. g. trapped ions and cavity QED, boosting theoretical and experimental decoherence studies.Comment: Published versio

Decoherence by electromagnetic fluctuations in double-quantum-dot charge qubits

We discuss decoherence due to electromagnetic fluctuations in charge qubits formed by two lateral quantum dots. We use an effective circuit model to evaluate correlations of voltage fluctuations in the qubit setup. These correlations allows us to estimate energy (T1) and phase (T2) relaxation times of the the qubit system. Our theoretical estimate of the quality factor due to dephasing by electromagnetic fluctuations yields values much higher than those found in recent experiments, indicating that other sources of decoherence play a dominant role.Comment: 12 pages, 5 figure

Numerical method for non-linear steady-state transport in one-dimensional correlated conductors

We present a method for investigating the steady-state transport properties of one-dimensional correlated quantum systems. Using a procedure based on our analysis of finite-size effects in a related classical model (LC line) we show that stationary currents can be obtained from transient currents in finite systems driven out of equilibrium. The non-equilibrium dynamics of correlated quantum systems is calculated using the time-evolving block decimation method. To demonstrate our method we determine the full I-V characteristic of the spinless fermion model with nearest-neighbour hopping t_H and interaction V_H using two different setups to generate currents (turning on/off a potential bias). Our numerical results agree with exact results for non-interacting fermions (V_H=0). For interacting fermions we find that in the linear regime eV << 4t_H the current I is independent from the setup and our numerical data agree with the predictions of the Luttinger liquid theory combined with the Bethe Ansatz solution. For larger potentials V the steady-state current depends on the current-generating setup and as V increases we find a negative differential conductance with one setup while the currents saturate at finite values in the other one. Both effects are due to finite renormalized bandwidths.Comment: published versio

Theory of superconductor-insulator transition in single Josephson junctions

A non-band theory is developed to describe the superconductor-insulator (SI) transtition in resistively shunted, single Josephson junctions. The $I-V$ characteristic is formulated by a Landauer-like formula and evaluated by the path-integral transfer-matrix method. The result is consistent with the recent experiments at around 80 $mK$. However, the insulator phase shrinks with decreasing temperature indicating that the single Josephson junction becomes all superconducting at absolute zero temperature, as long as dissipation is present.Comment: 4 pages, 3 figure

Phase-space theory for dispersive detectors of superconducting qubits

Motivated by recent experiments, we study the dynamics of a qubit quadratically coupled to its detector, a damped harmonic oscillator. We use a complex-environment approach, explicitly describing the dynamics of the qubit and the oscillator by means of their full Floquet state master equations in phase-space. We investigate the backaction of the environment on the measured qubit and explore several measurement protocols, which include a long-term full read-out cycle as well as schemes based on short time transfer of information between qubit and oscillator. We also show that the pointer becomes measurable before all information in the qubit has been lost.Comment: 15 pages, 8 figure