69 research outputs found
Generation and sampling of quantum states of light in a silicon chip
Implementing large instances of quantum algorithms requires the processing of
many quantum information carriers in a hardware platform that supports the
integration of different components. While established semiconductor
fabrication processes can integrate many photonic components, the generation
and algorithmic processing of many photons has been a bottleneck in integrated
photonics. Here we report the on-chip generation and processing of quantum
states of light with up to eight photons in quantum sampling algorithms.
Switching between different optical pumping regimes, we implement the
Scattershot, Gaussian and standard boson sampling protocols in the same silicon
chip, which integrates linear and nonlinear photonic circuitry. We use these
results to benchmark a quantum algorithm for calculating molecular vibronic
spectra. Our techniques can be readily scaled for the on-chip implementation of
specialised quantum algorithms with tens of photons, pointing the way to
efficiency advantages over conventional computers
Constellation Shaping for WDM systems using 256QAM/1024QAM with Probabilistic Optimization
In this paper, probabilistic shaping is numerically and experimentally
investigated for increasing the transmission reach of wavelength division
multiplexed (WDM) optical communication system employing quadrature amplitude
modulation (QAM). An optimized probability mass function (PMF) of the QAM
symbols is first found from a modified Blahut-Arimoto algorithm for the optical
channel. A turbo coded bit interleaved coded modulation system is then applied,
which relies on many-to-one labeling to achieve the desired PMF, thereby
achieving shaping gain. Pilot symbols at rate at most 2% are used for
synchronization and equalization, making it possible to receive input
constellations as large as 1024QAM. The system is evaluated experimentally on a
10 GBaud, 5 channels WDM setup. The maximum system reach is increased w.r.t.
standard 1024QAM by 20% at input data rate of 4.65 bits/symbol and up to 75% at
5.46 bits/symbol. It is shown that rate adaptation does not require changing of
the modulation format. The performance of the proposed 1024QAM shaped system is
validated on all 5 channels of the WDM signal for selected distances and rates.
Finally, it was shown via EXIT charts and BER analysis that iterative
demapping, while generally beneficial to the system, is not a requirement for
achieving the shaping gain.Comment: 10 pages, 12 figures, Journal of Lightwave Technology, 201
Demonstration of 5.1 Tbit/s data capacity on a single-wavelength channel
We have generated a single-wavelength data signal with a data capacity of 5.1 Tbit/s. The enabling techniques to generate the data signal are optical time-division multiplexing up to a symbol rate of 1.28 Tbaud, differential quadrature phase shift keying as data format, and polarisation-multiplexing. For the first time, error-free performance with a bit error rate less than 10-9 is demonstrated for the 5.1 Tbit/s data signal. This is achieved in a back-to-back configuration using a direct detection receiver based on polarisation- and time-demultiplexing, delay-demodulation and balanced photo-detection.</p
Air-core fiber distribution of hybrid vector vortex-polarization entangled states
Entanglement distribution between distant parties is one of the most
important and challenging tasks in quantum communication. Distribution of
photonic entangled states using optical fiber links is a fundamental building
block towards quantum networks. Among the different degrees of freedom, orbital
angular momentum (OAM) is one of the most promising due to its natural
capability to encode high dimensional quantum states. In this article, we
experimentally demonstrate fiber distribution of hybrid polarization-vector
vortex entangled photon pairs. To this end, we exploit a recently developed
air-core fiber which supports OAM modes. High fidelity distribution of the
entangled states is demonstrated by performing quantum state tomography in the
polarization-OAM Hilbert space after fiber propagation, and by violations of
Bell inequalities and multipartite entanglement tests. The present results open
new scenarios for quantum applications where correlated complex states can be
transmitted by exploiting the vectorial nature of light
Path-encoded high-dimensional quantum communication over a 2 km multicore fiber
Quantum key distribution (QKD) protocols based on high-dimensional quantum
states have shown the route to increase the key rate generation while
benefiting of enhanced error tolerance, thus overcoming the limitations of
two-dimensional QKD protocols. Nonetheless, the reliable transmission through
fiber links of high-dimensional quantum states remains an open challenge that
must be addressed to boost their application. Here, we demonstrate the reliable
transmission over a 2 km long multicore fiber of path-encoded high-dimensional
quantum states. Leveraging on a phase-locked loop system, a stable
interferometric detection is guaranteed, allowing for low error rates and the
generation of 6.3 Mbit/s of secret key rate.Comment: to appear in npj Quantum Informatio
Generalized Time-bin Quantum Random Number Generator with Uncharacterized Devices
Random number generators (RNG) based on quantum mechanics are captivating due to their security and unpredictability compared to conventional generators, such as pseudo-random number generators and hardware-random number generators. This work analyzes evolutions in the extractable amount of randomness with increasing the Hilbert space dimension, state preparation subspace, or measurement subspace in a class of semi-device-independent quantum-RNG, where bounding the states' overlap is the core assumption, built on the prepare-and-measure scheme. We further discuss the effect of these factors on the complexity and draw a conclusion on the optimal scenario. We investigate the generic case of time-bin encoding scheme, define various input (state preparation) and outcome (measurement) subspaces, and discuss the optimal scenarios to obtain maximum entropy. Several input designs were experimentally tested and analyzed for their conceivable outcome arrangements. We evaluated their performance by considering the device's imperfections, particularly the after-pulsing effect and dark counts of the detectors. Finally, we demonstrate that this approach can boost the system entropy, resulting in more extractable randomness
Multidimensional quantum entanglement with large-scale integrated optics
The ability to control multidimensional quantum systems is key for the
investigation of fundamental science and for the development of advanced
quantum technologies. Here we demonstrate a multidimensional integrated quantum
photonic platform able to robustly generate, control and analyze
high-dimensional entanglement. We realize a programmable bipartite entangled
system with dimension up to on a large-scale silicon-photonics
quantum circuit. The device integrates more than 550 photonic components on a
single chip, including 16 identical photon-pair sources. We verify the high
precision, generality and controllability of our multidimensional technology,
and further exploit these abilities to demonstrate key quantum applications
experimentally unexplored before, such as quantum randomness expansion and
self-testing on multidimensional states. Our work provides a prominent
experimental platform for the development of multidimensional quantum
technologies.Comment: Science, (2018
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