arXiv subjects

E. Strambini

Publications and source records attributed to E. Strambini.

24 records · Page 2Linked to original sources

arXiv2015

Geometric reduction of dynamical nonlocality in nanoscale quantum circuits

Nonlocality is a key feature discriminating quantum and classical physics. Quantum-interference phenomena, such as Young's double slit experiment, are one of the clearest manifestations of nonlocality, recently addressed as $dynamical$ to specify its origin in the quantum equations of motion. It is well known that loss of dynamical nonlocality can occur due to (partial) collapse of the wavefunction due to a measurement, such as which-path detection. However, alternative mechanisms affecting dynamical nonlocality have hardly been considered, although of crucial importance in many schemes for quantum information processing. Here, we present a fundamentally different pathway of losing dynamical nonlocality, demonstrating that the detailed geometry of the detection scheme is crucial to preserve nonlocality. By means of a solid-state quantum-interference experiment we quantify this effect in a diffusive system. We show that interference is not only affected by decoherence, but also by a loss of dynamical nonlocality based on a local reduction of the number of quantum conduction channels of the interferometer. With our measurements and theoretical model we demonstrate that this mechanism is an intrinsic property of quantum dynamics. Understanding the geometrical constraints protecting nonlocality is crucial when designing quantum networks for quantum information processing.

cond-mat.mes-hall↗

arXiv2014

Proximity nanovalve with large phase-tunable thermal conductance

We propose a phase-controlled heat-flux quantum valve based on the proximity effect driven by a superconducting quantum interference proximity transistor (SQUIPT). Its operation relies on the phase-dependent quasiparticle density of states in the Josephson weak-link of the SQUIPT which controls thermal transport across the device. In a realistic Al/Cu-based setup the structure can provide efficient control of thermal current inducing temperature swings exceeding $\sim100$~mK, and flux-to-temperature transfer coefficients up to $\sim 500$~mK/$Φ_0$ below 100~mK. The nanovalve performances improve by lowering the bath temperature, making the proposed structure a promising building-block for the implementation of coherent caloritronic devices operating below 1~K.

cond-mat.mes-hall↗

arXiv2013

High-contrast Aharonov-Bohm oscillations in the acoustoelectric transport regime

Phase-coherent acoustoelectric transport is reported.Aharonov-Bohm oscillations in the acoustoelectric current with visibility exceeding 100% were observed in mesoscopic GaAs rings as a function of an external magnetic field at cryogenic temperatures. A theoretical analysis of the acoustoelectric transport in ballistic devices is proposed to model experimental observations. Our findings highlight a close analogy between acoustoelectric transport and thermoelectric properties in ballistic devices.

cond-mat.mes-hall↗

arXiv2010

Electronic implementations of Interaction-Free Measurements

Three different implementations of interaction-free measurements (IFMs) in solid-state nanodevices are discussed. The first one is based on a series of concatenated Mach-Zehnder interferometers, in analogy to optical-IFM setups. The second one consists of a single interferometer and concatenation is achieved in the time domain making use of a quantized electron emitter. The third implementation consists of an asymmetric Aharonov-Bohm ring. For all three cases we show that the presence of a dephasing source acting on one arm of the interferometer can be detected without degrading the coherence of the measured current. Electronic implementations of IFMs in nanoelectronics may play a fundamental role as very accurate and noninvasive measuring schemes for quantum devices.

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arXiv2009

Coherent detection of electron dephasing

We show that an Aharonov-Bohm (AB) ring with asymmetric electron injection can act as a coherent detector of electron dephasing. The presence of a dephasing source in one of the two arms of a moderately-to-highly asymmetric ring changes the response of the system from total reflection to complete transmission while preserving the coherence of the electrons propagating from the ring, even for strong dephasing. We interpret this phenomenon as an implementation of an interaction-free measurement.

cond-mat.mes-hall↗

arXiv2009

Impact of classical forces and decoherence in multi-terminal Aharonov-Bohm networks

Multi-terminal Aharonov-Bohm (AB) rings are ideal building blocks for quantum networks (QNs) thanks to their ability to map input states into controlled coherent superpositions of output states. We report on experiments performed on three-terminal GaAs/Al_(x)Ga_(1-x)As AB devices and compare our results with a scattering-matrix model including Lorentz forces and decoherence. Our devices were studied as a function of external magnetic field (B) and gate voltage at temperatures down to 350 mK. The total output current from two terminals while applying a small bias to the third lead was found to be symmetric with respect to B with AB oscillations showing abrupt phase jumps between 0 and pi at different values of gate voltage and at low magnetic fields, reminiscent of the phase-rigidity constraint due to Onsager-Casimir relations. Individual outputs show quasi-linear dependence of the oscillation phase on the external electric field. We emphasize that a simple scattering-matrix approach can not model the observed behavior and propose an improved description that can fully describe the observed phenomena. Furthermore, we shall show that our model can be successfully exploited to determine the range of experimental parameters that guarantee a minimum oscillation visibility, given the geometry and coherence length of a QN.

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