1,595 research outputs found
Experimental Realization of a One-way Quantum Computer Algorithm Solving Simon's Problem
We report an experimental demonstration of a one-way implementation of a
quantum algorithm solving Simon's Problem - a black box period-finding problem
which has an exponential gap between the classical and quantum runtime. Using
an all-optical setup and modifying the bases of single-qubit measurements on a
five-qubit cluster state, key representative functions of the logical two-qubit
version's black box can be queried and solved. To the best of our knowledge,
this work represents the first experimental realization of the quantum
algorithm solving Simon's Problem. The experimental results are in excellent
agreement with the theoretical model, demonstrating the successful performance
of the algorithm. With a view to scaling up to larger numbers of qubits, we
analyze the resource requirements for an n-qubit version. This work helps
highlight how one-way quantum computing provides a practical route to
experimentally investigating the quantum-classical gap in the query complexity
model.Comment: 9 pages, 5 figure
Photon pair generation using four-wave mixing in a microstructured fibre: theory versus experiment
We develop a theoretical analysis of four-wave mixing used to generate photon
pairs useful for quantum information processing. The analysis applies to a
single mode microstructured fibre pumped by an ultra-short coherent pulse in
the normal dispersion region. Given the values of the optical propagation
constant inside the fibre, we can estimate the created number of photon pairs
per pulse, their central wavelength and their respective bandwidth. We use the
experimental results from a picosecond source of correlated photon pairs using
a micro-structured fibre to validate the model. The fibre is pumped in the
normal dispersion regime at 708nm and phase matching is satisfied for widely
spaced parametric wavelengths of 586nm and 894nm. We measure the number of
photons per pulse using a loss-independent coincidence scheme and compare the
results with the theoretical expectation. We show a good agreement between the
theoretical expectations and the experimental results for various fibre lengths
and pump powers.Comment: 23 pages, 9 figure
Experimental demonstration of a graph state quantum error-correction code
Scalable quantum computing and communication requires the protection of
quantum information from the detrimental effects of decoherence and noise.
Previous work tackling this problem has relied on the original circuit model
for quantum computing. However, recently a family of entangled resources known
as graph states has emerged as a versatile alternative for protecting quantum
information. Depending on the graph's structure, errors can be detected and
corrected in an efficient way using measurement-based techniques. In this
article we report an experimental demonstration of error correction using a
graph state code. We have used an all-optical setup to encode quantum
information into photons representing a four-qubit graph state. We are able to
reliably detect errors and correct against qubit loss. The graph we have
realized is setup independent, thus it could be employed in other physical
settings. Our results show that graph state codes are a promising approach for
achieving scalable quantum information processing
Two-photon interference between disparate sources for quantum networking
Quantum networks involve entanglement sharing between multiple users.
Ideally, any two users would be able to connect regardless of the type of
photon source they employ, provided they fulfill the requirements for
two-photon interference. From a theoretical perspective, photons coming from
different origins can interfere with a perfect visibility, provided they are
made indistinguishable in all degrees of freedom. Previous experimental
demonstrations of such a scenario have been limited to photon wavelengths below
900 nm, unsuitable for long distance communication, and suffered from low
interference visibility. We report two-photon interference using two disparate
heralded single photon sources, which involve different nonlinear effects,
operating in the telecom wavelength range. The measured visibility of the
two-photon interference is 80+/-4%, which paves the way to hybrid universal
quantum networks
Experimental characterization of universal one-way quantum computing
We report the characterization of a universal set of logic gates for one-way quantum computing using a four-photon 'star' cluster state generated by fusing photons from two independent photonic crystal fibre sources. We obtain a fidelity for the cluster state of 0.66 ± 0.01 with respect to the ideal case. We perform quantum process tomography to completely characterize a controlled-NOT, Hadamard and T gate all on the same compact entangled resource. Together, these operations make up a universal set of gates such that arbitrary quantum logic can be efficiently constructed from combinations of them. We find process fidelities with respect to the ideal cases of 0.64 ± 0.01 for the CNOT, 0.67 ± 0.03 for the Hadamard and 0.76 ± 0.04 for the T gate. The characterization of these gates enables the simulation of larger protocols and algorithms. As a basic example, we simulate a Swap gate consisting of three concatenated CNOT gates. Our work provides some pragmatic insights into the prospects for building up to a fully scalable and fault-tolerant one-way quantum computer with photons in realistic conditions
Experimental characterization of photonic fusion using fiber sources
We report the fusion of photons from two independent photonic crystal fiber
sources into polarization entangled states using a fiber-based polarizing beam
splitter. We achieve fidelities of up to F = 0.74 0.01 with respect to
the maximally entangled Bell state \phi+ using a low pump power of 5.3mW with a
success rate of 3.2 four-fold detections per second. By increasing the pump
power we find that success rates of up to 111.6 four-folds per second can be
achieved, with entanglement still present in the fused state. We characterize
the fusion operation by providing a full quantum process reconstruction. Here a
model is developed to describe the generation of entanglement, including the
main causes of imperfection, and we show that this model fits well with the
experimental results. Our work shows how non-ideal settings limit the success
of the fusion, providing useful information about the practical requirements
for an operation that may be used to build large entangled states in bulk and
on-chip quantum photonic waveguides.Comment: 19 pages, 4 figure
A new light at the end of the tunnel: fiber gas discharge lasers
Optical fibers have emerged as a transformative platform for building better
and more robust solid state lasers. However, the wavelengths available to these
lasers are limited. Using hollow core optical fibers allows us to add gases as
new potential gain media for fiber lasers, and also liberates the gas laser
from the limits normally imposed by diffraction. To demonstrate the new
technology, we present a fiber laser at 3500 nm wavelength, using an
antiresonant guiding hollow core optical fiber containing neutral xenon atoms
pumped by an afterglow discharge of a helium-xenon mixture within a fiber of
over 1 m in length. Laser action is confirmed through observation of
polarization dependence, mode pulling and mode beating. Our results unlock a
new breed of flexible fiber lasers operating at a plethora of wavelengths, many
previous unavailable.Comment: 10 page
Quantum teleportation and entanglement swapping with linear optics logic gates
We report on the usage of a linear optics phase gate for distinguishing all
four Bell states simultaneously in a quantum teleportation and entanglement
swapping protocol. This is demonstrated by full state tomography of the one and
two qubit output states of the two protocols, yielding average state fidelities
of about 0.83 and 0.77, respectively. In addition, the performance of the
teleportation channel is characterised by quantum process tomography. The non
classical properties of the entanglement swapping output states are further
confirmed by the violation of a CHSH-type Bell inequality of 2.14 on average.Comment: 11 pages, 3 figure
Absolute Frequency Measurements of the Hg^+ and Ca Optical Clock Transitions with a Femtosecond Laser
The frequency comb created by a femtosecond mode-locked laser and a
microstructured fiber is used to phase coherently measure the frequencies of
both the Hg^+ and Ca optical standards with respect to the SI second as
realized at NIST. We find the transition frequencies to be f_Hg=1 064 721 609
899 143(10) Hz and f_Ca=455 986 240 494 158(26) Hz, respectively. In addition
to the unprecedented precision demonstrated here, this work is the precursor to
all-optical atomic clocks based on the Hg^+ and Ca standards. Furthermore, when
combined with previous measurements, we find no time variations of these atomic
frequencies within the uncertainties of |(df_Ca/dt)/f_Ca| < 8 x 10^{-14}
yr^{-1}, and |(df_Hg/dt)/f_Hg|< 30 x 10^{-14} yr^{-1}.Comment: 6 pages, including 4 figures. RevTex 4. Submitted to Phys. Rev. Let
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