2,601 research outputs found
Non-equilibrium correlations and entanglement in a semiconductor hybrid circuit-QED system
We present a theoretical study of a hybrid circuit-QED system composed of two
semiconducting charge-qubits confined in a microwave resonator. The qubits are
defined in terms of the charge states of two spatially separated double quantum
dots (DQDs) which are coupled to the same photon mode in the microwave
resonator. We analyze a transport setup where each DQD is attached to
electronic reservoirs and biased out-of-equilibrium by a large voltage, and
study how electron transport across each DQD is modified by the coupling to the
common resonator. In particular, we show that the inelastic current through
each DQD reflects an indirect qubit-qubit interaction mediated by off-resonant
photons in the microwave resonator. As a result of this interaction, both
charge qubits stay entangled in the steady (dissipative) state. Finite shot
noise cross-correlations between currents across distant DQDs are another
manifestation of this nontrivial steady-state entanglement.Comment: Final versio
Non-hermitian topology as a unifying framework for the Andreev versus Majorana states controversy
Zero-energy Andreev levels in hybrid semiconductor-superconductor nanowires mimic all expected Majorana phenomenology, including 2 e2∕ h conductance quantisation, even where band topology predicts trivial phases. This surprising fact has been used to challenge the interpretation of various transport experiments in terms of Majorana zero modes. Here we show that the Andreev versus Majorana controversy is clarified when framed in the language of non-Hermitian topology, the natural description for quantum systems open to the environment. This change of paradigm allows one to understand topological transitions and the emergence of zero modes in more general systems than can be described by band topology. This is achieved by studying exceptional point bifurcations in the complex spectrum of the system’s non-Hermitian Hamiltonian. Within this broader topological classification, Majoranas from both conventional band topology and a large subset of Andreev levels at zero energy are in fact topologically equivalent, which explains why they cannot be distinguishedWe thank J. Cayao for useful discussions in the early stages of this work. Research supported by the Spanish Ministry of Science, Innovation and Universities through Grants PGC2018-097018-B-I00, FIS2015-65706-P, FIS2015-64654-P, FIS2016-80434-P (AEI/FEDER, EU), the FPI programme BES-2016-078122, the Ramón y Cajal programme Grants RYC-2011-09345, RYC-2013-14645, the MarÃa de Maeztu Programme for Units of Excellence in R&D (MDM-2014-0377), and the European Union’s Horizon 2020 research and innovation programme under the FETOPEN Grant Agreement No. 828948. We also acknowledge support from CSIC Research Platform on Quantum Technologies PTI-00
Quantum versus classical counting in nonMarkovian master equations
We discuss the description of full counting statistics in quantum transport
with a nonMarkovian master equation. We focus on differences arising from
whether charge is considered as a classical or a quantum degree of freedom.
These differences manifest themselves in the inhomogeneous term of the master
equation which describes initial correlations. We describe the influence on
current and in particular, the finite-frequency shotnoise. We illustrate these
ideas by studying transport through a quantum dot and give results that include
both sequential and cotunneling processes. Importantly, the noise spectra
derived from the classical description are essentially frequency-independent
and all quantum noise effects are absent. These effects are fully recovered
when charge is considered as a quantum degree of freedom.Comment: 12 pages; 3 figure
Emergence of Bulk CsCl Structure in (CsCl)nCs+ Cluster Ions
The emergence of CsCl bulk structure in (CsCl)nCs+ cluster ions is
investigated using a mixed quantum-mechanical/semiempirical theoretical
approach. We find that rhombic dodecahedral fragments (with bulk CsCl symmetry)
are more stable than rock-salt fragments after the completion of the fifth
rhombic dodecahedral atomic shell. From this size (n=184) on, a new set of
magic numbers should appear in the experimental mass spectra. We also propose
another experimental test for this transition, which explicitely involves the
electronic structure of the cluster. Finally, we perform more detailed
calculations in the size range n=31--33, where recent experimental
investigations have found indications of the presence of rhombic dodecahedral
(CsCl)32Cs+ isomers in the cluster beams.Comment: LaTeX file. 6 pages and 4 pictures. Accepted for publication in Phys.
Rev.
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