44,587 research outputs found
Off-diagonal geometric phase in composite systems
The effect due to the inter-subsystem coupling on the off-diagonal geometric
phase in a composite system is investigated. We analyze the case where the
system undergo an adiabatic evolution. Two coupled qubits driven by
time-dependent external magnetic fields are presented as an example, the
off-diagonal geometric phase as well as the adiabatic condition are examined
and discussed
Effects of microscopic strain distribution on Ga(1-x)In(x)As quantum wires grown by strain-induced lateral ordering
Band Structures and optical matrix elements of quantum wires(QWR's) made of
short-period superlattices(SPS) with strain-induced lateral ordering(SILO) are
investigated theoretically via an effective bond-orbital model(EBOM) combined
with a valence-force field(VFF) model. Valence-band anistropy, band mixing, and
effects due to local strain distribution at the atomistic level are all taken
into account. In particular, Ga(1-x)In(x)As QWR's grown by SILO process are
considered. A VFF model is used to find the equilibrium atomic positions in the
SILO QWR structure by minimizing the lattice energy. The strain tensor at each
atomic(In or GA) site is then obtained and included in the calculations of
electronic states and optical peroperties. It is found that different local
arrangement of atoms leads to very different strain distribution, which in term
alters the optical properties. In particular, we found that the optical
anisotropy can be reversed due to the change in shear strain caused by the
inter-change of atomic positions. Good agreement with the existing experimental
data on band gap and optical anisotropy can be obtained when a 2D alloy
structure with lateral composition modulation in the InAs/GaAs interface planes
of the SPS is used. Our studies revealed the possibility of "shear-strain
engineering" in SILO QWR light-emitting devices to achieve desired optical
anisotropy.Comment: 15 pages and 25 figures, some figures are relabe
Experimental realization of secure multi-party computation in an entanglement access to network
To construct a quantum network with many end users, it is critical to have a
cost-efficient way to distribute entanglement over different network ends. We
demonstrate an entanglement access network, where the expensive resource, the
entangled photon source at the telecom wavelength and the core communication
channel, is shared by many end users. Using this cost-efficient entanglement
access network, we report experimental demonstration of a secure multiparty
computation protocol, the privacy-preserving secure sum problem, based on the
network quantum cryptography
Quantum teleportation from light beams to vibrational states of a macroscopic diamond
With the recent development of optomechanics, the vibration in solids,
involving collective motion of trillions of atoms, gradually enters into the
realm of quantum control. Built on the recent remarkable progress in optical
control of motional states of diamonds, here we report an experimental
demonstration of quantum teleportation from light beams to vibrational states
of a macroscopic diamond under ambient conditions. Through quantum process
tomography, we demonstrate average teleportation fidelity (90.6+/- 1.0)%,
clearly exceeding the classical limit of 2/3. The experiment pushes the target
of quantum teleportation to the biggest object so far, with interesting
implications for optomechanical quantum control and quantum information
science.Comment: 7 pages, 4 figure
Exploring Quantum Contextuality to Generate True Random Numbers
Random numbers represent an indispensable resource for many applications. A
recent remarkable result is the realization that non-locality in quantum
mechanics can be used to certify genuine randomness through Bell's theorem,
producing reliable random numbers in a device independent way. Here, we explore
the contextuality aspect of quantum mechanics and show that true random numbers
can be generated using only single qutrit (three-state systems) without
entanglement and non-locality. In particular, we show that any observed
violation of the Klyachko-Can-Binicioglu-Shumovsky (KCBS) inequality [Phys.
Rev. Lett. 101, 20403 (2008)] provides a positive lower bound on genuine
randomness. As a proof-of-concept experiment, we demonstrate with photonic
qutrits that at least 5246 net true random numbers are generated with a
confidence level of 99.9%.Comment: Paper : 4.5 pages, 4 figures; Supplementary material : 5 pages, 2
figure
Experimental demonstration of a quantum router
The router is a key element for a network. We describe a scheme to realize
genuine quantum routing of single-photon pulses based on cascading of
conditional quantum gates in a Mach-Zehnder interferometer and report a
proof-of-principle experiment for its demonstration using linear optics quantum
gates. The polarization of the control photon routes in a coherent way the path
of the signal photon while preserving the qubit state of the signal photon
represented by its polarization. We demonstrate quantum nature of this router
by showing entanglement generated between the initially unentangled control and
signal photons, and confirm that the qubit state of the signal photon is well
preserved by the router through quantum process tomography
Experimental Hamiltonian Learning of An 11-qubit Solid-State Quantum Spin Register
Learning Hamiltonian of a quantum system is indispensable for prediction of
the system dynamics and realization of high fidelity quantum gates. However, it
is a significant challenge to efficiently characterize the Hamiltonian when its
Hilbert space dimension grows exponentially with the system size. Here, we
experimentally demonstrate an adaptive method to learn the effective
Hamiltonian of an 11-qubit quantum system consisting of one electron spin and
ten nuclear spins associated with a single Nitrogen-Vacancy center in a
diamond. We validate the estimated Hamiltonian by designing universal quantum
gates based on the learnt Hamiltonian parameters and demonstrate high-fidelity
gates in experiment. Our experimental demonstration shows a well-characterized
11-qubit quantum spin register with the ability to test quantum algorithms and
to act as a multi-qubit single node in a quantum network.Comment: 13 pages, 6 figure
Observation of topological links associated with Hopf insulators in a solid-state quantum simulator
Hopf insulators are intriguing three-dimensional topological insulators
characterized by an integer topological invariant. They originate from the
mathematical theory of Hopf fibration and epitomize the deep connection between
knot theory and topological phases of matter, which distinguishes them from
other classes of topological insulators. Here, we implement a model Hamiltonian
for Hopf insulators in a solid-state quantum simulator and report the first
experimental observation of their topological properties, including fascinating
topological links associated with the Hopf fibration and the integer-valued
topological invariant obtained from a direct tomographic measurement. Our
observation of topological links and Hopf fibration in a quantum simulator
opens the door to probe rich topological properties of Hopf insulators in
experiments. The quantum simulation and probing methods are also applicable to
the study of other intricate three-dimensional topological model Hamiltonians.Comment: including supplementary material
Observation of entanglement sudden death and rebirth by controlling solid-state spin bath
Quantum entanglement, the essential resource for quantum information
processing, has rich dynamics under different environments. Probing different
entanglement dynamics typically requires exquisite control of complicated
system-environment coupling in real experimental systems. Here, by a simple
control of the effective solid-state spin bath in a diamond sample, we observe
rich entanglement dynamics, including the conventional asymptotic decay as well
as the entanglement sudden death, a term coined for the phenomenon of complete
disappearance of entanglement after a short finite time interval. Furthermore,
we observe counter-intuitive entanglement rebirth after its sudden death in the
same diamond sample by tuning an experimental parameter, demonstrating that we
can conveniently control the non-Markovianity of the system-environment
coupling through a natural experimental knob. Further tuning of this
experimental knob can make the entanglement dynamics completely coherent under
the same environmental coupling. Probing of entanglement dynamics, apart from
its fundamental interest, may find applications in quantum information
processing through control of the environmental coupling
Reply to Comment on "State-independent experimental test of quantum contextuality in an indivisible system"
This is a reply to the comment from E. Amselem et al. on our paper (Phys.
Rev. Lett. 109, 150401 (2012), arXiv:1207.0059).Comment: 1 page, 1 figure, to appear in Phys. Rev. Lett. 201
- …