21 research outputs found
Phonon emission and arrival times of electrons from a single-electron source
In recent charge-pump experiments, single electrons are injected into quantum Hall edge channels at energies significantly above the Fermi level. We consider here the relaxation of these hot edge-channel electrons through longitudinal-optical-phonon emission. Our results show that the probability for an electron in the outermost edge channel to emit one or more phonons en route to a detector some microns distant along the edge channel suffers a double-exponential suppression with increasing magnetic field. This explains recent experimental observations. We also describe how the shape of the arrival-time distribution of electrons at the detector reflects the velocities of the electronic states post phonon emission. We show how this can give rise to pronounced oscillations in the arrival-time-distribution width as a function of magnetic field or electron energy
Picosecond coherent electron motion in a silicon single-electron source
Understanding ultrafast coherent electron dynamics is necessary for
application of a single-electron source to metrological standards, quantum
information processing, including electron quantum optics, and quantum sensing.
While the dynamics of an electron emitted from the source has been extensively
studied, there is as yet no study of the dynamics inside the source. This is
because the speed of the internal dynamics is typically higher than 100 GHz,
beyond state-of-the-art experimental bandwidth. Here, we theoretically and
experimentally demonstrate that the internal dynamics in a silicon
singleelectron source comprising a dynamic quantum dot can be detected,
utilising a resonant level with which the dynamics is read out as
gate-dependent current oscillations. Our experimental observation and
simulation with realistic parameters show that an electron wave packet
spatially oscillates quantum-coherently at 200 GHz inside the source.
Our results will lead to a protocol for detecting such fast dynamics in a
cavity and offer a means of engineering electron wave packets. This could allow
high-accuracy current sources, high-resolution and high-speed
electromagnetic-field sensing, and high-fidelity initialisation of flying
qubits
Minimax optimization of entanglement witness operator for the quantification of three-qubit mixed-state entanglement
We develop a numerical approach for quantifying entanglement in mixed quantum
states by convex-roof entanglement measures, based on the optimal entanglement
witness operator and the minimax optimization method. Our approach is
applicable to general entanglement measures and states and is an efficient
alternative to the conventional approach based on the optimal pure-state
decomposition. Compared with the conventional one, it has two important merits:
(i) that the global optimality of the solution is quantitatively verifiable,
and (ii) that the optimization is considerably simplified by exploiting the
common symmetry of the target state and measure. To demonstrate the merits, we
quantify Greenberger-Horne-Zeilinger (GHZ) entanglement in a class of
three-qubit full-rank mixed states composed of the GHZ state, the W state, and
the white noise, the simplest mixtures of states with different genuine
multipartite entanglement, which have not been quantified before this work. We
discuss some general properties of the form of the optimal witness operator and
of the convex structure of mixed states, which are related to the symmetry and
the rank of states
Partition of Two Interacting Electrons by a Potential Barrier
7 pages (including references)+ 7 pages (supplemental material), more
discussions includedScattering or tunneling of an electron at a potential barrier is a fundamental quantum effect. Electron-electron interactions often affect the scattering, and understanding of the interaction effect is crucial in detection of various phenomena of electron transport and their application to electron quantum optics. We theoretically study the partition and collision of two interacting hot electrons at a potential barrier. We predict their kinetic energy change by their Coulomb interaction during the scattering delay time inside the barrier. The energy change results in characteristic deviation of the partition probabilities from the noninteracting case. The derivation includes nonmonotonic dependence of the probabilities on the barrier height, which qualitatively agrees with recent experiments, and reduction of the fermionic antibunching.This work is supported by Korea NRF via the SRC Center for Quantum Coherence in Condensed Matter (Grant No. 2016R1A5A1008184). S. R. acknowledges partial support from the MarÃa de Maeztu Program for Units of Excellence No. MDM2017-0711 funded by MCIN/AEI/10.13039/501100011033.Peer reviewe
Partition of Two Interacting Electrons by a Potential Barrier
Scattering or tunneling of an electron at a potential barrier is a fundamental quantum effect. Electron-electron interactions often affect the scattering, and understanding of the interaction effect is crucial in detection of various phenomena of electron transport and their application to electron quantum optics. We theoretically study the partition and collision of two interacting hot electrons at a potential barrier in the quantum Hall regime. We predict their kinetic energy change by their Coulomb interaction during the scattering delay time inside the barrier. The energy change results in characteristic deviation of the partition probabilities from the noninteracting case. The derivation includes nonmonotonic dependence of the probabilities on the barrier height, which agrees with recent experiments, and reduction of the fermionic antibunching.This work is supported by Korea NRF via the SRC Center for Quantum Coherence in Condensed Matter (Grant No. 2016R1A5A1008184). S. R. acknowledges partial support from the MarÃa de Maeztu Program for Units of Excellence No. MDM2017-0711 funded by MCIN/AEI/10.13039/501100011033.N
Quantum consensus dynamics by entangling Maxwell demon
We introduce a Maxwell demon which generates many-body entanglement robustly against bit-flip noises, allowing us to obtain quantum advantage. Adopting the protocol of the voter model used for opinion dynamics approaching consensus, the demon randomly selects a qubit pair and performs a quantum feedback control, in continuous repetitions. We derive upper bounds for the entropy reduction and the work extraction rates by the demon's operation. These bounds are determined by a competition between the quantum–classical mutual information acquired by the demon and the absolute irreversibility of the feedback control. Our finding of the upper bounds corresponds to a reformulation of the second law of thermodynamics under a class of Maxwell demon which generates many-body entanglement in a working substance. This suggests that a general condition for the operation of a successful entangling demon, one for which many-body entanglement stabilization and work extraction are possible, is that the information gain is larger than the absolute irreversibility.We acknowledge support from projects PACSS RTI2018-093732-B-C21, QuTTNAQMa PID2020-117347GB-I00, and the Maria de Maeztu Program for Centers and Units of Excellence in R&D, Grant MDM-2017-0711 funded by MCIN/AEI/10.13039/501100011033 and by EU through FEDER funds. Support from GOIB project MACTOPE PDR2020-12 is acknowledged. SR also acknowledges partial support from National Research Foundation of Korea (Grant No. 2021R1A6A3A03040076).Peer reviewe
Quantum consensus dynamics by entangling Maxwell demon
We introduce a Maxwell demon which generates many-body entanglement robustly against bit-flip noises, which allows us to obtain quantum advantage. Adopting the protocol of the voter model used for opinion dynamics approaching consensus, the demon randomly selects a qubit pair and performs a quantum feedback control, in continuous repetitions. We derive upper bounds of the entropy reduction and the work extraction rates by demon's operation, which are determined by a competition between the quantum-classical mutual information acquired by the demon and the absolute irreversibility of the feedback control. Our finding of the upper bounds corresponds to a reformulation of the second law of thermodynamics under a class of Maxwell demon which generates many-body entanglement in a working substance.We acknowledge support from projects PACSS RTI2018-093732-B-C21, QuTTNAQMa PID2020-117347GB-I00, and the Maria de Maeztu Program for Centers and Units of Excellence in R&D, Grant MDM-2017-0711 funded by MCIN/AEI/10.13039/501100011033 and by EU through FEDER funds. Support from GOIB project MACTOPE PDR2020-12 is acknowledged. SR also acknowledges partial support from National Research Foundation of Korea (Grant No. 2021R1A6A3A03040076).N
Quantum Consensus Dynamics by Entangling Maxwell Demo
Trabajo presentado en el IFISC Poster Party (online).-- The IFISC Poster Party is an annual activity where PhD students and postdoctoral researchers of IFISC present their research in a poster format.-- Transport and Information in Quantum Systems.We introduce a Maxwell demon which generates many-body-entanglement robustly against thermal fluctuations, which allows us to obtain quantum advantage.
Adopting the protocol of the voter model used for opinion dynamics approaching consensus,
the demon randomly selects a qubit pair and performs a quantum feed back control, in continuous repetitions.
We derive a lower bound of the entropy production rate by demon’s operation,
which is determined by a competition between the quantum-classical mutual information acquired by the demon and the absolute irreversibility of the feedback control.
Our finding of the lower bound corresponds to a reformulation of the second law of thermodynamics under a stochastic and continuous quantum feedback control.Peer reviewe
Conductance of electrostatic wire junctions in bilayer graphene
9 pages, 7 figures, PRB acceptedThe conductance of electrostatic wire junctions in bilayer graphene, classified as trivial-trivial or trivial-topological regarding the confinement character on each junction side, is calculated. The topological side always corresponds to a kink-antikink system, as required for a proper connection with a trivial side. We report a conductance quench of the trivial-topological junction, with a conductance {\it near} quantization to , which is only half of the maximum value allowed by the Chern number of a kink-antikink system. The analysis allowed us to uncover the existence of a chiral edge mode in the trivial wire under quite general conditions. A double junction, trivial-topological-trivial, displays periodic Fano-like conductance resonances
(dips or peaks) induced by the created topological loop.We acknowledge support from Grants No. MDM2017-0711 and No. PID2020-117347GB-I00 funded by MCIN/AEI/10.13039/501100011033, and Grant No. PDR2020-12 funded by GOIB.Peer reviewe