64 research outputs found
Near-ideal spontaneous photon sources in silicon quantum photonics
While integrated photonics is a robust platform for quantum information
processing, architectures for photonic quantum computing place stringent
demands on high quality information carriers. Sources of single photons that
are highly indistinguishable and pure, that are either near-deterministic or
heralded with high efficiency, and that are suitable for mass-manufacture, have
been elusive. Here, we demonstrate on-chip photon sources that simultaneously
meet each of these requirements. Our photon sources are fabricated in silicon
using mature processes, and exploit a novel dual-mode pump-delayed excitation
scheme to engineer the emission of spectrally pure photon pairs through
intermodal spontaneous four-wave mixing in low-loss spiralled multi-mode
waveguides. We simultaneously measure a spectral purity of ,
a mutual indistinguishably of , and intrinsic
heralding efficiency. We measure on-chip quantum interference with a visibility
of between heralded photons from different sources. These
results represent a decisive step for scaling quantum information processing in
integrated photonics
Structure, rotational dynamics, and superfluidity of small OCS-doped He clusters
The structural and dynamical properties of OCS molecules solvated in Helium
clusters are studied using reptation quantum Monte Carlo, for cluster sizes
n=3-20 He atoms. Computer simulations allow us to establish a relation between
the rotational spectrum of the solvated molecule and the structure of the He
solvent, and of both with the onset of superfluidity. Our results agree with a
recent spectroscopic study of this system, and provide a more complex and
detailed microscopic picture of this system than inferred from experiments.Comment: 4 pages. TeX (requires revtex4) + 3 ps figures (1 color
High-threshold quantum computing by fusing one-dimensional cluster states
We propose a measurement-based model for fault-tolerant quantum computation
that can be realised with one-dimensional cluster states and fusion
measurements only; basic resources that are readily available with scalable
photonic hardware. Our simulations demonstrate high thresholds compared with
other measurement-based models realized with basic entangled resources and
two-qubit fusion measurements. Its high tolerance to noise indicates that our
practical construction offers a promising route to scalable quantum computing
with quantum emitters and linear-optical elements.Comment: 9 pages, 7 figures, comments welcom
Optimising graph codes for measurement-based loss tolerance
Graph codes play an important role in photonic quantum technologies as they
provide significant protection against qubit loss, a dominant noise mechanism.
Here, we develop methods to analyse and optimise measurement-based tolerance to
qubit loss and computational errors for arbitrary graph codes. Using these
tools we identify optimised codes with up to 12 qubits and asymptotically-large
modular constructions. The developed methods enable significant benefits for
various photonic quantum technologies, as we illustrate with novel all-photonic
quantum repeater states for quantum communication and high-threshold
fusion-based schemes for fault-tolerant quantum computing
Loss-tolerant architecture for quantum computing with quantum emitters
We develop an architecture for measurement-based quantum computing using
photonic quantum emitters. The architecture exploits spin-photon entanglement
as resource states and standard Bell measurements of photons for fusing them
into a large spin-qubit cluster state. The scheme is tailored to emitters with
limited memory capabilities since it only uses an initial non-adaptive
(ballistic) fusion process to construct a fully percolated graph state of
multiple emitters. By exploring various geometrical constructions for fusing
entangled photons from deterministic emitters, we improve the photon loss
tolerance significantly compared to similar all-photonic schemes
Path-polarization hyperentangled and cluster states of photons on a chip
Encoding many qubits in different degrees of freedom (DOFs) of single photons
is one of the routes towards enlarging the Hilbert space spanned by a photonic
quantum state. Hyperentangled photon states (i.e. states showing entanglement
in multiple DOFs) have demonstrated significant implications for both
fundamental physics tests and quantum communication and computation. Increasing
the number of qubits of photonic experiments requires miniaturization and
integration of the basic elements and functions to guarantee the set-up
stability. This motivates the development of technologies allowing the precise
control of different photonic DOFs on a chip. We demonstrate the contextual use
of path and polarization qubits propagating within an integrated quantum
circuit. We tested the properties of four-qubit linear cluster states built on
both DOFs. Our results pave the way towards the full integration on a chip of
hybrid multiqubit multiphoton states.Comment: 7 pages, 7 figures, RevTex4-1, Light: Science & Applications
AAP:http://aap.nature-lsa.cn:8080/cms/accessory/files/AAP-lsa201664.pd
Experimental Bayesian Quantum Phase Estimation on a Silicon Photonic Chip
Quantum phase estimation is a fundamental subroutine in many quantum
algorithms, including Shor's factorization algorithm and quantum simulation.
However, so far results have cast doubt on its practicability for near-term,
non-fault tolerant, quantum devices. Here we report experimental results
demonstrating that this intuition need not be true. We implement a recently
proposed adaptive Bayesian approach to quantum phase estimation and use it to
simulate molecular energies on a Silicon quantum photonic device. The approach
is verified to be well suited for pre-threshold quantum processors by
investigating its superior robustness to noise and decoherence compared to the
iterative phase estimation algorithm. This shows a promising route to unlock
the power of quantum phase estimation much sooner than previously believed
Threshold detection statistics of bosonic states
In quantum photonics, threshold detectors, distinguishing between vacuum and
one or more photons, such as superconducting nanowires and avalanche
photodiodes, are routinely used to measure Fock and Gaussian states of light.
Despite being the standard measurement scheme, there is no general closed form
expression for measurement probabilities with threshold detectors, unless
accepting coarse approximations or combinatorially scaling summations. Here, we
present new matrix functions to fill this gap. We develop the Bristolian and
the loop Torontonian functions for threshold detection of Fock and displaced
Gaussian states, respectively, and connect them to each other and to existing
matrix functions. By providing a unified picture of bosonic statistics for most
quantum states of light, we provide novel tools for the design and analysis of
photonic quantum technologies.Comment: 14 pages, 2 figures, 1 tabl
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