424 research outputs found
Quantum Analog-Digital Conversion
Many quantum algorithms, such as Harrow-Hassidim-Lloyd (HHL) algorithm,
depend on oracles that efficiently encode classical data into a quantum state.
The encoding of the data can be categorized into two types; analog-encoding
where the data are stored as amplitudes of a state, and digital-encoding where
they are stored as qubit-strings. The former has been utilized to process
classical data in an exponentially large space of a quantum system, where as
the latter is required to perform arithmetics on a quantum computer. Quantum
algorithms like HHL achieve quantum speedups with a sophisticated use of these
two encodings. In this work, we present algorithms that converts these two
encodings to one another. While quantum digital-to-analog conversions have
implicitly been used in existing quantum algorithms, we reformulate it and give
a generalized protocol that works probabilistically. On the other hand, we
propose an deterministic algorithm that performs a quantum analog-to-digital
conversion. These algorithms can be utilized to realize high-level quantum
algorithms such as a nonlinear transformation of amplitude of a quantum state.
As an example, we construct a "quantum amplitude perceptron", a quantum version
of neural network, and hence has a possible application in the area of quantum
machine learning.Comment: 7 page
Effective squeezing enhancement via measurement-induced non-Gaussian operation and its application to dense coding scheme
We study the measurement-induced non-Gaussian operation on the single- and
two-mode \textit{Gaussian} squeezed vacuum states with beam splitters and
on-off type photon detectors, with which \textit{mixed non-Gaussian} states are
generally obtained in the conditional process. It is known that the
entanglement can be enhanced via this non-Gaussian operation on the two-mode
squeezed vacuum state. We show that, in the range of practical squeezing
parameters, the conditional outputs are still close to Gaussian states, but
their second order variances of quantum fluctuations and correlations are
effectively suppressed and enhanced, respectively. To investigate an
operational meaning of these states, especially entangled states, we also
evaluate the quantum dense coding scheme from the viewpoint of the mutual
information, and we show that non-Gaussian entangled state can be advantageous
compared with the original two-mode squeezed state.Comment: REVTeX4, 14 pages with 21 figure
Measurement-free topological protection using dissipative feedback
Protecting quantum information from decoherence due to environmental noise is
vital for fault-tolerant quantum computation. To this end, standard quantum
error correction employs parallel projective measurements of individual
particles, which makes the system extremely complicated. Here we propose
measurement-free topological protection in two dimension without any selective
addressing of individual particles. We make use of engineered dissipative
dynamics and feedback operations to reduce the entropy generated by decoherence
in such a way that quantum information is topologically protected. We calculate
an error threshold, below which quantum information is protected, without
assuming selective addressing, projective measurements, nor instantaneous
classical processing. All physical operations are local and translationally
invariant, and no parallel projective measurement is required, which implies
high scalability. Furthermore, since the engineered dissipative dynamics we
utilized has been well studied in quantum simulation, the proposed scheme can
be a promising route progressing from quantum simulation to fault-tolerant
quantum information processing.Comment: 17pages, 6 figure
Electron Identification and Energy Measurement with Emulsion Cloud Chamber
AbstractCharged particles undergo the Multiple Coulomb Scattering (MCS) when passing through a material. Their momentum can be estimated from the distribution of the scattering angle directly. Angle of electrons (or positrons) largely changes because of the energy loss in bremsstrahlung, and they are distinguished from other charged particles by making use of its feature. Electron energy is generally measured by counting of electromagnetic shower (e.m. shower) tracks in Emulsion Cloud Chamber (ECC), so enough absorber material is needed to develop the shower. In the range from sub-GeV to a few GeV, electrons don’t develop noticeable showers. In order to estimate the energy of electrons in this range with a limited material, we established the new method which is based on the scattering angle considering the energy loss in bremsstrahlung. From the Monte Carlo simulation (MC) data, which is generated by electron beam (0.5GeV, 1GeV, 2GeV) exposure to ECC, we derived the correlation between energy and scattering angle in each emulsion layer. We fixed the function and some parameters which 1GeV MC sample would return 1GeV as the center value, and then applied to 0.5GeV and 2GeV sample and confirmed the energy resolution about 50% within two radiation length
Unambiguous discrimination among oracle operators
We address the problem of unambiguous discrimination among oracle operators.
The general theory of unambiguous discrimination among unitary operators is
extended with this application in mind. We prove that entanglement with an
ancilla cannot assist any discrimination strategy for commuting unitary
operators. We also obtain a simple, practical test for the unambiguous
distinguishability of an arbitrary set of unitary operators on a given system.
Using this result, we prove that the unambiguous distinguishability criterion
is the same for both standard and minimal oracle operators. We then show that,
except in certain trivial cases, unambiguous discrimination among all standard
oracle operators corresponding to integer functions with fixed domain and range
is impossible. However, we find that it is possible to unambiguously
discriminate among the Grover oracle operators corresponding to an arbitrarily
large unsorted database. The unambiguous distinguishability of standard oracle
operators corresponding to totally indistinguishable functions, which possess a
strong form of classical indistinguishability, is analysed. We prove that these
operators are not unambiguously distinguishable for any finite set of totally
indistinguishable functions on a Boolean domain and with arbitrary fixed range.
Sets of such functions on a larger domain can have unambiguously
distinguishable standard oracle operators and we provide a complete analysis of
the simplest case, that of four functions. We also examine the possibility of
unambiguous oracle operator discrimination with multiple parallel calls and
investigate an intriguing unitary superoperator transformation between standard
and entanglement-assisted minimal oracle operators.Comment: 35 pages. Final version. To appear in J. Phys. A: Math. & Theo
Boosting computational power through spatial multiplexing in quantum reservoir computing
Quantum reservoir computing provides a framework for exploiting the natural
dynamics of quantum systems as a computational resource. It can implement
real-time signal processing and solve temporal machine learning problems in
general, which requires memory and nonlinear mapping of the recent input stream
using the quantum dynamics in computational supremacy region, where the
classical simulation of the system is intractable. A nuclear magnetic resonance
spin-ensemble system is one of the realistic candidates for such physical
implementations, which is currently available in laboratories. In this paper,
considering these realistic experimental constraints for implementing the
framework, we introduce a scheme, which we call a spatial multiplexing
technique, to effectively boost the computational power of the platform. This
technique exploits disjoint dynamics, which originate from multiple different
quantum systems driven by common input streams in parallel. Accordingly, unlike
designing a single large quantum system to increase the number of qubits for
computational nodes, it is possible to prepare a huge number of qubits from
multiple but small quantum systems, which are operationally easy to handle in
laboratory experiments. We numerically demonstrate the effectiveness of the
technique using several benchmark tasks and quantitatively investigate its
specifications, range of validity, and limitations in detail.Comment: 15 page
- …