17,386 research outputs found
Conserved charges in the quantum simulation of integrable spin chains
When simulating the time evolution of quantum many-body systems on a digital
quantum computer, one faces the challenges of quantum noise and of the Trotter
error due to time discretization. The Trotter error in integrable spin chains
can be under control if the discrete time evolution preserves integrability. In
this work we implement, on a real quantum computer and on classical simulators,
the integrable Trotterization of the spin-1/2 Heisenberg XXX spin chain. We
study how quantum noise affects the time evolution of several conserved
charges, and observe the decay of the expectation values. We in addition study
the early time behaviors of the time evolution, which can potentially be used
to benchmark quantum devices and algorithms in the future. We also provide an
efficient method to generate the conserved charges at higher orders.Comment: 26 pages, data and codes available at
https://github.com/takuoku/integrable-trotterizatio
Optical control of competing exchange interactions and coherent spin-charge coupling in two-orbital Mott insulators
In order to have a better understanding of ultrafast electrical control of
exchange interactions in multi-orbital systems, we study a two-orbital Hubbard
model at half filling under the action of a time-periodic electric field. Using
suitable projection operators and a generalized time-dependent canonical
transformation, we derive an effective Hamiltonian which describes two
different regimes. First, for a wide range of non-resonant frequencies, we find
a change of the bilinear Heisenberg exchange that is
analogous to the single-orbital case. Moreover we demonstrate that also the
additional biquadratic exchange interaction can be enhanced,
reduced and even change sign depending on the electric field. Second, for
special driving frequencies, we demonstrate a novel spin-charge coupling
phenomenon enabling coherent transfer between spin and charge degrees of
freedom of doubly ionized states. These results are confirmed by an exact
time-evolution of the full two-orbital Mott-Hubbard Hamiltonian.Comment: 3 pages, 6 figure
Tensor Product Approach to Quantum Control
In this proof-of-concept paper we show that tensor product approach is
efficient for control of large quantum systems, such as Heisenberg spin wires,
which are essential for emerging quantum computing technologies. We compute
optimal control sequences using GRAPE method, applying the recently developed
tAMEn algorithm to calculate evolution of quantum states represented in the
tensor train format to reduce storage. Using tensor product algorithms we can
overcome the curse of dimensionality and compute the optimal control pulse for
a 41 spin system on a single workstation with fully controlled accuracy and
huge savings of computational time and memory. The use of tensor product
algorithms opens new approaches for development of quantum computers with 50 to
100 qubits.Comment: To appear in Proc. IMSE 201
Hamiltonian quantum simulation with bounded-strength controls
We propose dynamical control schemes for Hamiltonian simulation in many-body
quantum systems that avoid instantaneous control operations and rely solely on
realistic bounded-strength control Hamiltonians. Each simulation protocol
consists of periodic repetitions of a basic control block, constructed as a
suitable modification of an "Eulerian decoupling cycle," that would otherwise
implement a trivial (zero) target Hamiltonian. For an open quantum system
coupled to an uncontrollable environment, our approach may be employed to
engineer an effective evolution that simulates a target Hamiltonian on the
system, while suppressing unwanted decoherence to the leading order. We present
illustrative applications to both closed- and open-system simulation settings,
with emphasis on simulation of non-local (two-body) Hamiltonians using only
local (one-body) controls. In particular, we provide simulation schemes
applicable to Heisenberg-coupled spin chains exposed to general linear
decoherence, and show how to simulate Kitaev's honeycomb lattice Hamiltonian
starting from Ising-coupled qubits, as potentially relevant to the dynamical
generation of a topologically protected quantum memory. Additional implications
for quantum information processing are discussed.Comment: 24 pages, 5 color figure
Entanglement of the Ising-Heisenberg diamond spin-1/2 cluster in evolution
In the last two decades, magnetic, thermodynamic properties and bipartite
thermal entanglement in diamond spin clusters and chains have been studied.
Such spin structures are presented in various compounds. The ions of
in the natural mineral azurite are arranged in a diamond spin chain. There are
no studies of the entanglement behaviour during the quantum evolution of such
systems. Herein, we consider the evolution of entanglement in the diamond
spin-1/2 cluster. This cluster consists of two central spins described by the
anisotropic Heisenberg model, which interact with two side spins via Ising
interaction. The influence of the interaction coupling with side spins on the
entanglement of central spins is investigated. It is shown that choosing the
value of this coupling allows us to control the behaviour of entanglement
between central spins. As a result, we find conditions for achieving the
maximal values of entanglement. In addition, the entanglement behaviour between
the side spins, central and side spins, and between a certain spin and the rest
of the system is studied. In these cases, the conditions for achieving maximal
entanglement are also obtained.Comment: 21 pages, 5 figure
Quantum simulation of the wavefunction to probe frustrated Heisenberg spin systems
Quantum simulators are controllable quantum systems that can reproduce the
dynamics of the system of interest, which are unfeasible for classical
computers. Recent developments in quantum technology enable the precise control
of individual quantum particles as required for studying complex quantum
systems. Particularly, quantum simulators capable of simulating frustrated
Heisenberg spin systems provide platforms for understanding exotic matter such
as high-temperature superconductors. Here we report the analog quantum
simulation of the ground-state wavefunction to probe arbitrary Heisenberg-type
interactions among four spin-1/2 particles . Depending on the interaction
strength, frustration within the system emerges such that the ground state
evolves from a localized to a resonating valence-bond state. This spin-1/2
tetramer is created using the polarization states of four photons. The
single-particle addressability and tunable measurement-induced interactions
provide us insights into entanglement dynamics among individual particles. We
directly extract ground-state energies and pair-wise quantum correlations to
observe the monogamy of entanglement
Low-control and robust quantum refrigerator and applications with electronic spins in diamond
We propose a general protocol for low-control refrigeration and thermometry
of thermal qubits, which can be implemented using electronic spins in diamond.
The refrigeration is implemented by a probe, consisting of a network of
interacting spins. The protocol involves two operations: (i) free evolution of
the probe; and (ii) a swap gate between one spin in the probe and the thermal
qubit we wish to cool. We show that if the initial state of the probe falls
within a suitable range, and the free evolution of the probe is both unital and
conserves the excitation in the -direction, then the cooling protocol will
always succeed, with an efficiency that depends on the rate of spin dephasing
and the swap gate fidelity. Furthermore, measuring the probe after it has
cooled many qubits provides an estimate of their temperature. We provide a
specific example where the probe is a Heisenberg spin chain, and suggest a
physical implementation using electronic spins in diamond. Here the probe is
constituted of nitrogen vacancy (NV) centers, while the thermal qubits are dark
spins. By using a novel pulse sequence, a chain of NV centers can be made to
evolve according to a Heisenberg Hamiltonian. This proposal allows for a range
of applications, such as NV-based nuclear magnetic resonance of photosensitive
molecules kept in a dark spot on a sample, and it opens up possibilities for
the study of quantum thermodynamics, environment-assisted sensing, and
many-body physics
Quantum Phase Transition of Ground-state Entanglement in a Heisenberg Spin Chain Simulated in an NMR Quantum Computer
Using an NMR quantum computer, we experimentally simulate the quantum phase
transition of a Heisenberg spin chain. The Hamiltonian is generated by a
multiple pulse sequence, the nuclear spin system is prepared in its
(pseudo-pure) ground state and the effective Hamiltonian varied in such a way
that the Heisenberg chain is taken from a product state to an entangled state
and finally to a different product state.Comment: 5 pages, 5 eps figures. Accepted in Phys. Rev.
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