3,151 research outputs found
Quantum generative adversarial learning
Generative adversarial networks (GANs) represent a powerful tool for
classical machine learning: a generator tries to create statistics for data
that mimics those of a true data set, while a discriminator tries to
discriminate between the true and fake data. The learning process for generator
and discriminator can be thought of as an adversarial game, and under
reasonable assumptions, the game converges to the point where the generator
generates the same statistics as the true data and the discriminator is unable
to discriminate between the true and the generated data. This paper introduces
the notion of quantum generative adversarial networks (QuGANs), where the data
consists either of quantum states, or of classical data, and the generator and
discriminator are equipped with quantum information processors. We show that
the unique fixed point of the quantum adversarial game also occurs when the
generator produces the same statistics as the data. Since quantum systems are
intrinsically probabilistic the proof of the quantum case is different from -
and simpler than - the classical case. We show that when the data consists of
samples of measurements made on high-dimensional spaces, quantum adversarial
networks may exhibit an exponential advantage over classical adversarial
networks.Comment: 5 pages, 1 figur
Quantum Hopfield neural network
Quantum computing allows for the potential of significant advancements in
both the speed and the capacity of widely used machine learning techniques.
Here we employ quantum algorithms for the Hopfield network, which can be used
for pattern recognition, reconstruction, and optimization as a realization of a
content-addressable memory system. We show that an exponentially large network
can be stored in a polynomial number of quantum bits by encoding the network
into the amplitudes of quantum states. By introducing a classical technique for
operating the Hopfield network, we can leverage quantum algorithms to obtain a
quantum computational complexity that is logarithmic in the dimension of the
data. We also present an application of our method as a genetic sequence
recognizer.Comment: 13 pages, 3 figures, final versio
Quantum algorithm for non-homogeneous linear partial differential equations
We describe a quantum algorithm for preparing states that encode solutions of
non-homogeneous linear partial differential equations. The algorithm is a
continuous-variable version of matrix inversion: it efficiently inverts
differential operators that are polynomials in the variables and their partial
derivatives. The output is a quantum state whose wavefunction is proportional
to a specific solution of the non-homogeneous differential equation, which can
be measured to reveal features of the solution. The algorithm consists of three
stages: preparing fixed resource states in ancillary systems, performing
Hamiltonian simulation, and measuring the ancilla systems. The algorithm can be
carried out using standard methods for gate decompositions, but we improve this
in two ways. First, we show that for a wide class of differential operators, it
is possible to derive exact decompositions for the gates employed in
Hamiltonian simulation. This avoids the need for costly commutator
approximations, reducing gate counts by orders of magnitude. Additionally, we
employ methods from machine learning to find explicit circuits that prepare the
required resource states. We conclude by studying an example application of the
algorithm: solving Poisson's equation in electrostatics.Comment: 9 pages, 6 figure
How Massless Neutrinos Affect the Cosmic Microwave Background Damping Tail
We explore the physical origin and robustness of constraints on the energy
density in relativistic species prior to and during recombination, often
expressed as constraints on an effective number of neutrino species, Neff.
Constraints from current data combination of Wilkinson Microwave Anisotropy
Probe (WMAP) and South Pole Telescope (SPT) are almost entirely due to the
impact of the neutrinos on the expansion rate, and how those changes to the
expansion rate alter the ratio of the photon diffusion scale to the sound
horizon scale at recombination. We demonstrate that very little of the
constraining power comes from the early Integrated Sachs-Wolfe (ISW) effect,
and also provide a first determination of the amplitude of the early ISW
effect. Varying the fraction of baryonic mass in Helium, Yp, also changes the
ratio of damping to sound-horizon scales. We discuss the physical effects that
prevent the resulting near-degeneracy between Neff and Yp from being a complete
one. Examining light element abundance measurements, we see no significant
evidence for evolution of Neff and the baryon-to-photon ratio from the epoch of
big bang nucleosynthesis to decoupling. Finally, we consider measurements of
the distance-redshift relation at low to intermediate redshifts and their
implications for the value of Neff.Comment: 11 pages. Replaced version extends our discussion of origin of
constraints and updates for current data, submitted to PR
Automated precision alignment of optical components for hydroxide catalysis bonding
We describe an interferometric system that can measure the alignment and separation of a polished face of a optical component and an adjacent polished surface. Accuracies achieved are ∼ 1μrad for the relative angles in two orthogonal directions and ∼ 30μm in separation. We describe the use of this readout system to automate the process of hydroxide catalysis bonding of a fused-silica component to a fused-silica baseplate. The complete alignment and bonding sequence was typically achieved in a timescale of a few minutes, followed by an initial cure of 10 minutes. A series of bonds were performed using two fluids - a simple sodium hydroxide solution and a sodium hydroxide solution with some sodium silicate solution added. In each case we achieved final bonded component angular alignment within 10 μrad and position in the critical direction within 4 μm of the planned targets. The small movements of the component during the initial bonding and curing phases were monitored. The bonds made using the sodium silicate mixture achieved their final bonded alignment over a period of ∼ 15 hours. Bonds using the simple sodium hydroxide solution achieved their final alignment in a much shorter time of a few minutes. The automated system promises to speed the manufacture of precision-aligned assemblies using hydroxide catalysis bonding by more than an order of magnitude over the more manual approach used to build the optical interferometer at the heart of the recent ESA LISA Pathfinder technology demonstrator mission. This novel approach will be key to the time-efficient and low-risk manufacture of the complex optical systems needed for the forthcoming ESA spaceborne gravitational waves observatory mission, provisionally named LISA
A compendium of Colombian policing challenges : from Pablo to present
Colombia has one of the oldest democracies in Latin American, however it has a history of violence that stretches from the time of the breakup of Gran Colombia. Simón BolÃvar’s vision started to erode in the 1830s and ended in 1903 with the independence of Panama. Contemporary Colombia saw violence continue with peasant revolts in the 1920s and 30s, la Violencia in the 1940s, the formation of the insurgent groups like the FARC and ELN in the 1960s, the creation of drug cartels in the 1970s and their transformation into narco-terrorist groups and then micro traffickers in the 1980s and 1990s. There have been limited periods of peace for the citizens of Colombia.
These events have consequently challenged Colombia's judiciary and police forces in the areas of general violence, inequality, geographical policing challenges, corruption, case backlog and Colombian police leadership. As former president Belisario Betancur states, 'Modern times have not been easy for Colombia' (1998, p.XV).
The challenges in writing this thesis have been considerable. This author has utilised experience gained from living and working in Colombia for over five and a half years and the experience of his protected sources as well as the foundations laid by other academics and the media in order to present the most significant of the challenges to Colombian policing in the last forty years. The goal of this document is to form a compendium on these areas for those who are new to Colombian policing, its judiciary and the history that has helped to shape them
MDI-QKD: Continuous- versus discrete-variables at metropolitan distances
In a comment, Xu, Curty, Qi, Qian, and Lo claimed that discrete-variable (DV)
measurement device independent (MDI) quantum key distribution (QKD) would
compete with its continuous-variable (CV) counterpart at metropolitan
distances. Actually, Xu et al.'s analysis supports exactly the opposite by
showing that the experimental rate of our CV protocol (achieved with practical
room-temperature devices) remains one order of magnitude higher than their
purely-numerical and over-optimistic extrapolation for qubits, based on
nearly-ideal parameters and cryogenic detectors (unsuitable solutions for a
realistic metropolitan network, which is expected to run on cheap
room-temperature devices, potentially even mobile). The experimental rate of
our protocol (expressed as bits per relay use) is confirmed to be two-three
orders of magnitude higher than the rate of any realistic simulation of
practical DV-MDI-QKD over short-medium distances. Of course this does not mean
that DV-MDI-QKD networks should not be investigated or built, but increasing
their rate is a non-trivial practical problem clearly beyond the analysis of Xu
et al. Finally, in order to clarify the facts, we also refute a series of
incorrect arguments against CV-MDI-QKD and, more generally, CV-QKD, which were
made by Xu et al. with the goal of supporting their thesis.Comment: Updated reply to Xu, Curty, Qi, Qian and Lo (arXiv:1506.04819),
including a point-to-point rebuttal of their new "Appendix E: Addendum
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