arXiv subjects

David Oehri

Publications and source records attributed to David Oehri.

6 recordsLinked to original sources

arXiv2018

Long-range spin-coherence in a strongly-coupled all electronic dot-cavity system

We present a theoretical analysis of spin-coherent electronic transport across a mesoscopic dot-cavity system. Such spin-coherent transport has been recently demonstrated in an experiment with a dot-cavity hybrid implemented in a high-mobility two-dimensional electron gas [C. Rössler et al., Phys. Rev. Lett. 115, 166603 (2015)] and its spectroscopic signatures have been interpreted in terms of a competition between Kondo-type dot-lead and molecular-type dot-cavity singlet-formation. Our analysis brings forward all the transport features observed in the experiments and supports the claim that a spin-coherent molecular singlet forms across the full extent of the dot-cavity device. Our model analysis includes: (i) a single-particle numerical investigation of the two-dimensional geometry, its quantum-coral-type eigenstates and associated spectroscopic transport features, (ii) the derivation of an effective interacting model based on the observations of the numerical and experimental studies, and (iii) the prediction of transport characteristics through the device using a combination of a master-equation approach on top of exact eigenstates of the dot-cavity system, and an equation-of-motion analysis that includes Kondo physics. The latter provides additional temperature scaling predictions for the many-body phase transition between molecular- and Kondo-singlet formation and its associated transport signatures.

cond-mat.mes-hall↗

arXiv2016

Time correlators from deferred measurements

Repeated measurements as typically occurring in two- or multi-time correlators rely on von Neumann's projection postulate, telling how to restart the system after an intermediate measurement. We invoke the principle of deferred measurement to describe an alternative procedure where co-evolving quantum memories extract system information through entanglement, combined with a final readout of the memories described by Born's rule. The new approach to repeated quantum measurements respects the unitary evolution of quantum mechanics during intermediate times, unifies the treatment of strong and weak measurements, and reproduces the projected and (anti-) symmetrized correlators in the two limits. As an illustration, we apply our formalism to the calculation of the electron charge correlator in a mesoscopic physics setting, where single electron pulses assume the role of flying memory qubits. We propose an experimental setup which reduces the measurement of the time correlator to the measurement of currents and noise, exploiting the (pulsed) injection of electrons to cope with the challenge of performing short-time measurements.

cond-mat.mes-hall↗

arXiv2015

Transport Spectroscopy of a Spin-Coherent Dot-Cavity System

Quantum engineering requires controllable artificial systems with quantum coherence exceeding the device size and operation time. This can be achieved with geometrically confined low-dimensional electronic structures embedded within ultraclean materials, with prominent examples being artificial atoms (quantum dots) and quantum corrals (electronic cavities). Combining the two structures, we implement a mesoscopic coupled dot-cavity system in a high-mobility two-dimensional electron gas, and obtain an extended spin-singlet state in the regime of strong dot-cavity coupling. Engineering such extended quantum states presents a viable route for nonlocal spin coupling that is applicable for quantum information processing.

cond-mat.mes-hall↗

arXiv2014

A tunable, nonlinear Hong-Ou-Mandel interferometer

We investigate the two-photon scattering properties of a Jaynes-Cummings (JC) nonlinearity consisting of a two-level system (qubit) interacting with a single mode cavity, which is coupled to two waveguides, each containing a single incident photon wave packet initially. In this scattering setup, we study the interplay between the Hong-Ou-Mandel effect arising due to quantum interference and effective photon-photon interactions induced by the presence of the qubit. We calculate the two-photon scattering matrix of this system analytically and identify signatures of interference and interaction in the second order auto- and cross-correlation functions of the scattered photons. In the dispersive regime, when qubit and cavity are far detuned from each other, we find that the JC nonlinearity can be used as an almost linear, in-situ tunable beam splitter giving rise to ideal Hong-Ou-Mandel interference, generating a highly path-entangled two-photon NOON state of the scattered photons. The latter manifests itself in strongly suppressed waveguide cross-correlations and Poissonian photon number statistics in each waveguide. If the two-level system and the cavity are on resonance, the JC nonlinearity strongly modifies the ideal HOM conditions leading to a smaller degree of path entanglement and sub-poissonian photon number statistics. In the latter regime, we find that photon blockade is associated with bunched auto-correlations in both waveguides, while a two-polariton resonance can lead to bunched as well as anti-bunched correlations.

quant-ph↗

arXiv2014

Projective versus weak measurement of charge in a mesoscopic conductor

We study the charge dynamics of a quantum dot as measured by a nearby quantum point contact probing the dot via individual single-particle wave packets. We contrast the two limiting cases of weak and strong system--detector coupling exerting vanishing and strong back-action on the system and analyze the resulting differences in the charge-charge correlator. Extending the study to multiple projective measurements modelling a continuous strong measurement, we identify a transition from a charge dynamics dominated by the system's properties to a universal dynamics governed by the measurement.

cond-mat.mes-hall↗

arXiv2012

Scattering matrix approach to interacting electron transport

We investigate the modification in mesoscopic electronic transport due to electron-electron interactions making use of scattering states. We demonstrate that for a specific (finite range) interaction kernel, the knowledge of the scattering matrix is sufficient to take interaction effects into account. We calculate perturbatively the corrections to the current and current-current correlator; in agreement with previous work, we find that, in linear response, interaction effects can be accounted for by an effective (renormalized) transmission probability. Beyond linear response, simple renormalization of scattering coefficients is not sufficient to describe the current-current correlator, as additional corrections arise due to irreducible two-particle processes. Furthermore, we find that the correlations between opposite-spin currents induced by interaction are enhanced for an asymmetric scatterer, generating a nonzero result already to lowest order in the interaction.

cond-mat.mes-hall↗