We demonstrate theoretically how photon-number statistics of a driven damped oscillator at finite temperature can be extracted by measuring the dephasing spectrum of a two-level system dispersively coupled to the oscillator; we thus extend the work of M. I. Dykman and M. A. Krivoglaz ͓Sov. Phys. Solid State 29, 210 ͑1987͔͒ and J. Gambetta et al. ͓Phys. Rev. A 74, 042318 ͑2006͔͒. We carefully consider the fidelity of this scheme-to what extent does the measurement reflect the initial number statistics of the mode? We also derive analytic results for the dephasing of a qubit by a driven thermal mode, and compare results obtained at different levels of approximation. Our results have relevance both to experiments in circuit cavity QED, as well as to nanoelectromechanical systems.
We describe the conditional and unconditional dynamics of two coupled quantum dots when one dot is subjected to a measurement of its occupation number by coupling it to a third readout dot via the Coulomb interaction. The readout dot is coupled to source and drain leads under weak bias, and a tunnel current flows through a single bound state when energetically allowed. The occupation of the quantum dot near the readout dot shifts the bound state of the readout dot from a low conducting state to a high conducting state. The measurement is made by continuously monitoring the tunnel current through the readout dot. We show that there is a difference between the time scale for the measurement-induced decoherence between the localized states of the dots, and the time scale on which the system becomes localized due to the measurement.
We describe a quantum electromechanical system comprising a single quantum dot harmonically bound between two electrodes and facilitating a tunneling current between them. An example of such a system is a fullerene molecule between two metal electrodes [Park et al., Nature 407, 57 (2000)]. The description is based on a quantum master equation for the density operator of the electronic and vibrational degrees of freedom and thus incorporates the dynamics of both diagonal (population) and off diagonal (coherence) terms. We derive coupled equations of motion for the electron occupation number of the dot and the vibrational degrees of freedom, including damping of the vibration and thermo-mechanical noise. This dynamical description is related to observable features of the system including the stationary current as a function of bias voltage.
We investigate the use of nanocrystal quantum dots as a quantum bus element for preparing various quantum resources for use in photonic quantum technologies. Using the Stark-tuning property of nanocrystal quantum dots as well as the biexciton transition, we demonstrate a photonic controlled-NOT ͑CNOT͒ interaction between two logical photonic qubits comprising two cavity field modes each. We find the CNOT interaction to be a robust generator of photonic Bell states, even with relatively large biexciton losses. These results are discussed in light of the current state of the art of both microcavity fabrication and recent advances in nanocrystal quantum dot technology. Overall, we find that such a scheme should be feasible in the near future with appropriate refinements to both nanocrystal fabrication technology and microcavity design. Such a gate could serve as an active element in photonic-based quantum technologies.
We study the electrical transport of a harmonically-bound, single-molecule C60shuttle operating in the Coulomb blockade regime, i.e. single electron shuttling. In particular we examine the dependance of the tunnel current on an ultra-small stationary force exerted on the shuttle. As an example we consider the force exerted on an endohedral N@C60by the magnetic field gradient generated by a nearby nanomagnet. We derive a Hamiltonian for the full shuttle system which includes the metallic contacts, the spatially dependent tunnel couplings to the shuttle, the electronic and motional degrees of freedom of the shuttle itself and a coupling of the shuttle's motion to a phonon bath. We analyse the resulting quantum master equation and find that, due to the exponential dependance of the tunnel probability on the shuttle-contact separation, the current is highly sensitive to very small forces. In particular we predict that the spin state of the endohedral electrons of N@C60in a large magnetic gradient field can be distinguished from the resulting current signals within a few tens of nanoseconds. This effect could prove useful for the detection of the endohedral spin-state of individual paramagnetic molecules such as N@C60and P@C60, or the detection of very small static forces acting on a C60shuttle.
International migration is usually motivated by economic reasons. However, many people also migrate overseas to continue studies in higher-level education. This paper analyses the role of Indonesian students abroad, especially those who are members of the Indonesian Student Association (PPI) in protecting Indonesian workers (TKI). The research is focused on PPI in the country with the highest number of Indonesian migrant workers, namely Malaysia. This study applied a qualitative approach to collect primary and secondary data. Primary data was collected through interviews, and secondary data was gained through literature review. The research shows that PPI, as an agent of change, has a role in protecting migrant workers. The PPI has various kinds of contributions such as expressing ideas and discourses to protect international migrant workers, becoming a mediator (in solving conflicts involving the workers), facilitating shelter, providing repatriation assistance, legal assistance and advocacy, as well as economic empowerment and education activities for migrant workers and their families.
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