6,134 research outputs found
(2+1) resonant enhanced multiphoton ionization of H_2 via the E, F^(1)ÎŁ^+_g state
In this paper, we report the results of ab initio calculations of photoelectron angular distributions and vibrational branching ratios for the (2+1) REMPI of H_2 via the E, F^(1)ÎŁ^+_g state, and compare these with the experimental data of Anderson et al. [Chem. Phys. Lett. 105, 22 (1984)]. These results show that the observed nonâFranckâCondon behavior is predominantly due to the R dependence of the transition matrix elements, and to a lesser degree to the energy dependence. This work presents the first molecular REMPI study employing a correlated wave function to describe the Rydbergâvalence mixing in the resonant intermediate state
Phonon-Assisted Two-Photon Interference from Remote Quantum Emitters
Photonic quantum technologies are on the verge offinding applications in everyday life with quantum cryptography andquantum simulators on the horizon. Extensive research has beencarried out to identify suitable quantum emitters and single epitaxialquantum dots have emerged as near-optimal sources of bright, on-demand, highly indistinguishable single photons and entangledphoton-pairs. In order to build up quantum networks, it is essentialto interface remote quantum emitters. However, this is still anoutstanding challenge, as the quantum states of dissimilarâartificialatomsâhave to be prepared on-demand with highfidelity and thegenerated photons have to be made indistinguishable in all possibledegrees of freedom. Here, we overcome this major obstacle and show an unprecedented two-photon interference (visibility of 51±5%) from remote strain-tunable GaAs quantum dots emitting on-demand photon-pairs. We achieve this result by exploiting forthefirst time the full potential of a novel phonon-assisted two-photon excitation scheme, which allows for the generation ofhighly indistinguishable (visibility of 71±9%) entangled photon-pairs (fidelity of 90±2%), enables push-button biexciton statepreparation (fidelity of 80±2%) and outperforms conventional resonant two-photon excitation schemes in terms of robustnessagainst environmental decoherence. Our results mark an important milestone for the practical realization of quantum repeatersand complex multiphoton entanglement experiments involving dissimilar artificial atom
Highly indistinguishable and strongly entangled photons from symmetric GaAs quantum dots
The development of scalable sources of non-classical light is fundamental to unlocking thetechnological potential of quantum photonics. Semiconductor quantum dots are emerging asnear-optimal sources of indistinguishable single photons. However, their performance assources of entangled-photon pairs are still modest compared to parametric down converters.Photons emitted from conventional StranskiâKrastanov InGaAs quantum dots have shownnon-optimal levels of entanglement and indistinguishability. For quantum networks, bothcriteria must be met simultaneously. Here, we show that this is possible with a system thathas received limited attention so far: GaAs quantum dots. They can emit triggered polar-ization-entangled photons with high purity (g(2)(0) = 0.002±0.002), high indistinguish-ability (0.93±0.07 for 2 ns pulse separation) and high entanglement fidelity(0.94±0.01). Our results show that GaAs might be the material of choice for quantum-dotentanglement sources in future quantum technologie
Design of a five-axis ultra-precision micro-milling machineâUltraMill. Part 2: Integrated dynamic modelling, design optimisation and analysis
Using computer models to predict the dynamic performance of ultra-precision machine tools can help manufacturers to substantially reduce the lead time and cost of developing new machines. However, the use of electronic drives on such machines is becoming widespread, the machine dynamic performance depending not only on the mechanical structure and components but also on the control system and electronic drives. Bench-top ultra-precision machine tools are highly desirable for the micro-manufacturing of high-accuracy micro-mechanical components. However, the development is still at the nascent stage and hence lacks standardised guidelines. Part 2 of this two-part paper proposes an integrated approach, which permits analysis and optimisation of the entire machine dynamic performance at the early design stage. Based on the proposed approach, the modelling and simulation process of a novel five-axis bench-top ultra-precision micro-milling machine toolâUltraMillâis presented. The modelling and simulation cover the dynamics of the machine structure, the moving components, the control system and the machining process and are used to predict the entire machine performance of two typical configurations
Network Models of Quantum Percolation and Their Field-Theory Representations
We obtain the field-theory representations of several network models that are
relevant to 2D transport in high magnetic fields. Among them, the simplest one,
which is relevant to the plateau transition in the quantum Hall effect, is
equivalent to a particular representation of an antiferromagnetic SU(2N) () spin chain. Since the later can be mapped onto a ,
sigma model, and since recent numerical analyses of the
corresponding network give a delocalization transition with ,
we conclude that the same exponent is applicable to the sigma model
Theory of high-order harmonic generation from molecules by intense laser pulses
We show that high-order harmonics generated from molecules by intense laser
pulses can be expressed as the product of a returning electron wave packet and
the photo-recombination cross section (PRCS) where the electron wave packet can
be obtained from simple strong-field approximation (SFA) or from a companion
atomic target. Using these wave packets but replacing the PRCS obtained from
SFA or from the atomic target by the accurate PRCS from molecules, the
resulting HHG spectra are shown to agree well with the benchmark results from
direct numerical solution of the time-dependent Schr\"odinger equation, for the
case of H in laser fields. The result illustrates that these powerful
theoretical tools can be used for obtaining high-order harmonic spectra from
molecules. More importantly, the results imply that the PRCS extracted from
laser-induced HHG spectra can be used for time-resolved dynamic chemical
imaging of transient molecules with temporal resolutions down to a few
femtoseconds.Comment: 10 pages, 5 figure
Universal relation between longitudinal and transverse conductivities in quantum Hall effect
We show that any critical transition region between two adjacent Hall
plateaus in either integer or fractional quantum Hall effect is characterized
by a universal semi-circle relationship between the longitudinal and transverse
conductivities, provided the sample is homogeneous and isotropic on a large
scale. This conclusion is demonstrated both for the phase-coherent quantum
transport as well as for the incoherent transport.Comment: REVTEX 3.0, 1 figure, 4 pages. SISSA-08179
Spin Star as Switch for Quantum Networks
Quantum state transfer is an important task in quantum information
processing. It is known that one can engineer the couplings of a
one-dimensional spin chain to achieve the goal of perfect state transfer. To
leverage the value of these spin chains, a spin star is potentially useful for
connecting different parts of a quantum network. In this work, we extend the
spin-chain engineering problem to the problems with a topology of a star
network. We show that a permanently coupled spin star can function as a network
switch for transferring quantum states selectively from one node to another by
varying the local potentials only. Together with one-dimensional chains, this
result allows applications of quantum state transfer be applied to more general
quantum networks.Comment: 10 pages, 2 figur
Liouvillian Approach to the Integer Quantum Hall Effect Transition
We present a novel approach to the localization-delocalization transition in
the integer quantum Hall effect. The Hamiltonian projected onto the lowest
Landau level can be written in terms of the projected density operators alone.
This and the closed set of commutation relations between the projected
densities leads to simple equations for the time evolution of the density
operators. These equations can be used to map the problem of calculating the
disorder averaged and energetically unconstrained density-density correlation
function to the problem of calculating the one-particle density of states of a
dynamical system with a novel action. At the self-consistent mean-field level,
this approach yields normal diffusion and a finite longitudinal conductivity.
While we have not been able to go beyond the saddle point approximation
analytically, we show numerically that the critical localization exponent can
be extracted from the energetically integrated correlation function yielding
in excellent agreement with previous finite-size scaling
studies.Comment: 9 pages, submitted to PR
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