9,643 research outputs found
Fast universal quantum gates on microwave photons with all-resonance operations in circuit QED
Stark shift on a superconducting qubit in circuit quantum electrodynamics
(QED) has been used to construct universal quantum entangling gates on
superconducting resonators in previous works. It is a second-order coupling
effect between the resonator and the qubit in the dispersive regime, which
leads to a slow state-selective rotation on the qubit. Here, we present two
proposals to construct the fast universal quantum gates on superconducting
resonators in a microwave-photon quantum processor composed of multiple
superconducting resonators coupled to a superconducting transmon qutrit, that
is, the controlled-phase (c-phase) gate on two microwave-photon resonators and
the controlled-controlled phase (cc-phase) gates on three resonators, resorting
to quantum resonance operations, without any drive field. Compared with
previous works, our universal quantum gates have the higher fidelities and
shorter operation times in theory. The numerical simulation shows that the
fidelity of our c-phase gate is 99.57% within about 38.1 ns and that of our
cc-phase gate is 99.25% within about 73.3 ns.Comment: 12 pages, 6 figures, 2 table
Quantum state transfer and controlled-phase gate on one-dimensional superconducting resonators assisted by a quantum bus
We propose a quantum processor for the scalable quantum computation on
microwave photons in distant one-dimensional superconducting resonators. It is
composed of a common resonator R acting as a quantum bus and some distant
resonators coupled to the bus in different positions assisted by
superconducting quantum interferometer devices (SQUID), different from previous
processors. R is coupled to one transmon qutrit, and the coupling strengths
between and R can be fully tuned by the external flux through the SQUID.
To show the processor can be used to achieve universal quantum computation
effectively, we present a scheme to complete the high-fidelity quantum state
transfer between two distant microwave-photon resonators and another one for
the high-fidelity controlled-phase gate on them. By using the technique for
catching and releasing the microwave photons from resonators, our processor may
play an important role in quantum communication as well.Comment: 11 pages, 4 figures, one colum
Universal quantum gates on microwave photons assisted by circuit quantum electrodynamics
Based on a microwave-photon quantum processor with two superconducting
resonators coupled to one transmon qutrit, we construct the controlled-phase
(c-phase) gate on microwave-photon-resonator qudits, by combination of the
photon-number-dependent frequency-shift effect on the transmon qutrit by the
first resonator and the resonant operation between the qutrit and the second
resonator. This distinct feature provides us a useful way to achieve the
c-phase gate on the two resonator qudits with a higher fidelity and a shorter
operation time, compared with the previous proposals. The fidelity of our
c-phase gate can reach 99.51% within 93 ns. Moreover, our device can be
extended easily to construct the three-qudit gates on three resonator qudits,
far different from the existing proposals. Our controlled-controlled-phase gate
on three resonator qudits is accomplished with the assistance of a transmon
qutrit and its fidelity can reach 92.92% within 124.64 ns.Comment: 9 pages, 5 figure
One-step implementation of entanglement generation on microwave photons in distant 1D superconducting resonators
We present a scalable quantum-bus-based device for generating the
entanglement on microwave photons (MPs) in distant superconducting resonators
(SRs). Different from the processors in previous works with some resonators
coupled to a superconducting qubit (SQ), our device is composed of some 1D SRs
which are coupled to the quantum bus (another common resonator ) in
its different positions simply, assisted by superconducting quantum
interferometer devices. By using the technique for catching and releasing a MP
state in a 1D SR, it can work as an entanglement generator or a node in quantum
communication. To demonstrate the performance of this device, we propose a
one-step scheme to generate high-fidelity Bell states on MPs in two distant
SRs. It works in the dispersive regime of and , which enables us to
extend it to generate high-fidelity multi-Bell states on different resonator
pairs simultaneously.Comment: 5 pages, 3 figure
From atomistic model to the Peierls-Nabarro model with -surface for dislocations
The Peierls-Nabarro (PN) model for dislocations is a hybrid model that
incorporates the atomistic information of the dislocation core structure into
the continuum theory. In this paper, we study the convergence from a full
atomistic model to the PN model with -surface for the dislocation in a
bilayer system (e.g. bilayer graphene). We prove that the displacement field of
and the total energy of the dislocation solution of the PN model are
asymptotically close to those of the full atomistic model. Our work can be
considered as a generalization of the analysis of the convergence from
atomistic model to Cauchy-Born rule for crystals without defects in the
literature.Comment: 45 pages, 2 figure
Self-Erasing Network for Integral Object Attention
Recently, adversarial erasing for weakly-supervised object attention has been
deeply studied due to its capability in localizing integral object regions.
However, such a strategy raises one key problem that attention regions will
gradually expand to non-object regions as training iterations continue, which
significantly decreases the quality of the produced attention maps. To tackle
such an issue as well as promote the quality of object attention, we introduce
a simple yet effective Self-Erasing Network (SeeNet) to prohibit attentions
from spreading to unexpected background regions. In particular, SeeNet
leverages two self-erasing strategies to encourage networks to use reliable
object and background cues for learning to attention. In this way, integral
object regions can be effectively highlighted without including much more
background regions. To test the quality of the generated attention maps, we
employ the mined object regions as heuristic cues for learning semantic
segmentation models. Experiments on Pascal VOC well demonstrate the superiority
of our SeeNet over other state-of-the-art methods.Comment: Accepted by NIPS201
Quantum information processing on nitrogen-vacancy ensembles with the local resonance assisted by circuit QED
With the local resonant interaction between a nitrogen-vacancy-center
ensemble (NVE) and a superconducting coplanar resonator, and the single-qubit
operation, we propose two protocols for the state transfer between two remote
NVEs and for fast controlled-phase (c-phase) on these NVEs, respectively. This
hybrid quantum system is composed of two distant NVEs coupled to separated
high-Q transmission line resonators (TLRs), which are interconnected by a
current-biased Josephsonjunction superconducting phase qubit. The fidelity of
our state-transfer protocol is about 99.65% within the operation time of 70.60
ns. The fidelity of our c-phase gate is about 98.23% within the operation time
of 93.87 ns. Furthermore, using the c-phase gate, we construct a
two-dimensional cluster state on NVEs in n*n square grid based on the hybrid
quantum system for the one-way quantum computation. Our protocol may be more
robust, compared with the one based on the superconducting resonators, due to
the long coherence time of NVEs at room temperature.Comment: 10 pages, 4 figure
Certification of Boson Sampling Devices with Coarse-Grained Measurements
A boson sampling device could efficiently sample from the output probability
distribution of noninteracting bosons undergoing many-body interference. This
problem is not only classically intractable, but its solution is also believed
to be classically unverifiable. Hence, a major difficulty in experiment is to
ensure a boson sampling device performs correctly. We present an experimental
friendly scheme to extract useful and robust information from the quantum boson
samplers based on coarse-grained measurements. The procedure can be applied to
certify the equivalence of boson sampling devices while ruling out alternative
fraudulent devices. We perform numerical simulations to demonstrate the
feasibility of the method and consider the effects of realistic noise. Our
approach is expected to be generally applicable to other many-body
certification tasks beyond the boson sampling problem.Comment: 8 pages including Supplemental Materials, 7 figures, 3 table
Classifying parafermionic gapped phases using matrix product states
In the Fock representation, we construct matrix product states (MPS) for
one-dimensional gapped phases for parafermions. From the
analysis of irreducibility of MPS, we classify all possible gapped phases of
parafermions without extra symmetry other than
charge symmetry, including topological phases, spontaneous
symmetry breaking phases and a trivial phase. For all phases, we find the
irreducible forms of local matrices of MPS, which span different kinds of
graded algebras. The topological phases are characterized by the non-trivial
simple graded algebras with the characteristic graded centers,
yielding the degeneracies of the full transfer matrix spectra uniquely. But the
spontaneous symmetry breaking phases correspond to the trivial semisimple
graded algebras, which can be further reduced to the trivial
simple graded algebras, where is the divisor of . So
the present results deepen our understanding of topological phases in one
dimension from the viewpoints of MPS.Comment: 12 pages, 1 figure, 2 tables, published versio
Matrix product states for topological phases with parafermions
In the Fock representation, we propose a framework to construct the
generalized matrix product states (MPS) for topological phases with parafermions. Unlike the Majorana fermions, the parafermions form intrinsically interacting systems. Here we
explicitly construct two topologically distinct classes of irreducible parafermionic MPS wave functions, characterized by one or two
parafermionic zero modes at each end of an open chain. Their corresponding
parent Hamiltonians are found as the fixed point models of the single
parafermion chain and two-coupled parafermion chains with
symmetry. Our results thus pave the road
to investigate all possible topological phases with
parafermions within the matrix product representation in one dimension.Comment: 10 pages, 4 figures, published versio
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