1,052 research outputs found
Robust interface between flying and topological qubits
Hybrid architectures, consisting of conventional and topological qubits, have
recently attracted much attention due to their capability in consolidating the
robustness of topological qubits and the universality of conventional qubits.
However, these two kinds of qubits are normally constructed in significantly
different energy scales, and thus this energy mismatch is a major obstacle for
their coupling that supports the exchange of quantum information between them.
Here, we propose a microwave photonic quantum bus for a direct strong coupling
between the topological and conventional qubits, in which the energy mismatch
is compensated by the external driving field via the fractional ac Josephson
effect. In the framework of tight-binding simulation and perturbation theory,
we show that the energy splitting of the topological qubits in a finite length
nanowire is still robust against local perturbations, which is ensured not only
by topology, but also by the particle-hole symmetry. Therefore, the present
scheme realizes a robust interface between the flying and topological qubits.
Finally, we demonstrate that this quantum bus can also be used to generate
multipartitie entangled states with the topological qubits.Comment: Accepted for publication in Scientific Report
Scattering Dynamics and Boundary States of a Non-Hermitian Dirac Equation
We study a non-Hermitian variant of the (2+1)-dimensional Dirac wave
equation, which hosts a real energy spectrum with pairwise-orthogonal
eigenstates. In the spatially uniform case, the Hamiltonian's non-Hermitian
symmetries allow its eigenstates to be mapped to a pair of Hermitian Dirac
subsystems. When a wave is transmitted across an interface between two
spatially uniform domains with different model parameters, an anomalous form of
Klein tunneling can occur, whereby reflection is suppressed while the
transmitted flux is substantially higher or lower than the incident flux. The
interface can even function as a simultaneous laser and coherent perfect
absorber. Remarkably, the violation of flux conservation occurs entirely at the
interface, as no wave amplification or damping takes place in the bulk.
Moreover, at energies within the Dirac mass gaps, the interface can support
exponentially localized boundary states with real energies. These features of
the continuum model can also be reproduced in non-Hermitian lattice models
Implementing universal nonadiabatic holonomic quantum gates with transmons
Geometric phases are well known to be noise-resilient in quantum
evolutions/operations. Holonomic quantum gates provide us with a robust way
towards universal quantum computation, as these quantum gates are actually
induced by nonabelian geometric phases. Here we propose and elaborate how to
efficiently implement universal nonadiabatic holonomic quantum gates on simpler
superconducting circuits, with a single transmon serving as a qubit. In our
proposal, an arbitrary single-qubit holonomic gate can be realized in a
single-loop scenario, by varying the amplitudes and phase difference of two
microwave fields resonantly coupled to a transmon, while nontrivial two-qubit
holonomic gates may be generated with a transmission-line resonator being
simultaneously coupled to the two target transmons in an effective resonant
way. Moreover, our scenario may readily be scaled up to a two-dimensional
lattice configuration, which is able to support large scalable quantum
computation, paving the way for practically implementing universal nonadiabatic
holonomic quantum computation with superconducting circuits.Comment: v3 Appendix added, v4 published version, v5 published version with
correction
Resonant peak splitting for ballistic conductance in magnetic superlattices
We investigate theoretically the resonant splitting of ballistic conductance
peaks in magnetic superlattices. It is found that, for magnetic superlattices
with periodically arranged identical magnetic-barriers, there exists a
general -fold resonant peak splitting rule for ballistic conductance,
which is the analogy of the -fold resonant splitting for transmission in
-barrier electric superlattices (R. Tsu and L. Esaki, Appl. Phys. Lett. {\bf
22}, 562 (1973)).Comment: 9 pages, 3 figures, latex forma
Cavity QED treatment of scattering-induced efficient free-space excitation and collection in high-Q whispering-gallery microcavities
Whispering-gallery microcavity laser possesses ultralow threshold, whereas
convenient free-space optical excitation and collection suffer from low
efficiencies due to its rotational symmetry. Here we analytically study a
three-dimensional microsphere coupled to a nano-sized scatterer in the
framework of quantum optics. It is found that the scatterer is capable of
coupling light in and out of the whispering-gallery modes (WGMs) without
seriously degrading their high-Q properties, while the microsphere itself plays
the role of a lens to focus the input beam on the scatterer and vice versa. Our
analytical results show that (1) the high-Q WGMs can be excited in free space,
and (2) over 50% of the microcavity laser emission can be collected within less
than . This coupling system holds great potential for low
threshold microlasers free of external couplers.Comment: 10 pages, 8 figure
Scheme for demonstrating Bell theorem in tripartite entanglement between atomic ensembles
We propose an experimentally feasible scheme to demonstrate quantum
nonlocality, using Greenberger-Horne-Zeilinger (GHZ) and entanglement
between atomic ensembles generated by a new developed method based on laser
manipulation and{} single-photon detection.Comment: 10 pages, 4 figure
Tunable interfaces for realizing universal quantum computation with topological qubits
We propose to implement tunable interfaces for realizing universal quantum
computation with topological qubits. One interface is between the topological
and superconducting qubits, which can realize arbitrary single-qubit gate on
the topological qubit. When two qubits are involved, the interface between the
topological qubits and a microwave cavity can induce a nontrivial two-qubit
gate, which can not be constructed based on braiding operations. The two
interfaces, being tunable via an external magnetic flux, may serve as the
building blocks towards universal quantum computation with topological qubits
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