17,057 research outputs found
Recommendations and illustrations for the evaluation of photonic random number generators
The never-ending quest to improve the security of digital information
combined with recent improvements in hardware technology has caused the field
of random number generation to undergo a fundamental shift from relying solely
on pseudo-random algorithms to employing optical entropy sources. Despite these
significant advances on the hardware side, commonly used statistical measures
and evaluation practices remain ill-suited to understand or quantify the
optical entropy that underlies physical random number generation. We review the
state of the art in the evaluation of optical random number generation and
recommend a new paradigm: quantifying entropy generation and understanding the
physical limits of the optical sources of randomness. In order to do this, we
advocate for the separation of the physical entropy source from deterministic
post-processing in the evaluation of random number generators and for the
explicit consideration of the impact of the measurement and digitization
process on the rate of entropy production. We present the Cohen-Procaccia
estimate of the entropy rate as one way to do this. In order
to provide an illustration of our recommendations, we apply the Cohen-Procaccia
estimate as well as the entropy estimates from the new NIST draft standards for
physical random number generators to evaluate and compare three common optical
entropy sources: single photon time-of-arrival detection, chaotic lasers, and
amplified spontaneous emission
Strong experimental guarantees in ultrafast quantum random number generation
We describe a methodology and standard of proof for experimental claims of
quantum random number generation (QRNG), analogous to well-established methods
from precision measurement. For appropriately constructed physical
implementations, lower bounds on the quantum contribution to the average
min-entropy can be derived from measurements on the QRNG output. Given these
bounds, randomness extractors allow generation of nearly perfect
"{\epsilon}-random" bit streams. An analysis of experimental uncertainties then
gives experimentally derived confidence levels on the {\epsilon} randomness of
these sequences. We demonstrate the methodology by application to
phase-diffusion QRNG, driven by spontaneous emission as a trusted randomness
source. All other factors, including classical phase noise, amplitude
fluctuations, digitization errors and correlations due to finite detection
bandwidth, are treated with paranoid caution, i.e., assuming the worst possible
behaviors consistent with observations. A data-constrained numerical
optimization of the distribution of untrusted parameters is used to lower bound
the average min-entropy. Under this paranoid analysis, the QRNG remains
efficient, generating at least 2.3 quantum random bits per symbol with 8-bit
digitization and at least 0.83 quantum random bits per symbol with binary
digitization, at a confidence level of 0.99993. The result demonstrates
ultrafast QRNG with strong experimental guarantees.Comment: 11 pages, 9 figure
Thermodynamics of quantum systems under dynamical control
In this review the debated rapport between thermodynamics and quantum
mechanics is addressed in the framework of the theory of
periodically-driven/controlled quantum-thermodynamic machines. The basic model
studied here is that of a two-level system (TLS), whose energy is periodically
modulated while the system is coupled to thermal baths. When the modulation
interval is short compared to the bath memory time, the system-bath
correlations are affected, thereby causing cooling or heating of the TLS,
depending on the interval. In steady state, a periodically-modulated TLS
coupled to two distinct baths constitutes the simplest quantum heat machine
(QHM) that may operate as either an engine or a refrigerator, depending on the
modulation rate. We find their efficiency and power-output bounds and the
conditions for attaining these bounds. An extension of this model to multilevel
systems shows that the QHM power output can be boosted by the multilevel
degeneracy.
These results are used to scrutinize basic thermodynamic principles: (i)
Externally-driven/modulated QHMs may attain the Carnot efficiency bound, but
when the driving is done by a quantum device ("piston"), the efficiency
strongly depends on its initial quantum state. Such dependence has been unknown
thus far. (ii) The refrigeration rate effected by QHMs does not vanish as the
temperature approaches absolute zero for certain quantized baths, e.g.,
magnons, thous challenging Nernst's unattainability principle. (iii)
System-bath correlations allow more work extraction under periodic control than
that expected from the Szilard-Landauer principle, provided the period is in
the non-Markovian domain. Thus, dynamically-controlled QHMs may benefit from
hitherto unexploited thermodynamic resources
Source-independent quantum random number generation
Quantum random number generators can provide genuine randomness by appealing
to the fundamental principles of quantum mechanics. In general, a physical
generator contains two parts---a randomness source and its readout. The source
is essential to the quality of the resulting random numbers; hence, it needs to
be carefully calibrated and modeled to achieve information-theoretical provable
randomness. However, in practice, the source is a complicated physical system,
such as a light source or an atomic ensemble, and any deviations in the
real-life implementation from the theoretical model may affect the randomness
of the output. To close this gap, we propose a source-independent scheme for
quantum random number generation in which output randomness can be certified,
even when the source is uncharacterized and untrusted. In our randomness
analysis, we make no assumptions about the dimension of the source. For
instance, multiphoton emissions are allowed in optical implementations. Our
analysis takes into account the finite-key effect with the composable security
definition. In the limit of large data size, the length of the input random
seed is exponentially small compared to that of the output random bit. In
addition, by modifying a quantum key distribution system, we experimentally
demonstrate our scheme and achieve a randomness generation rate of over
bit/s.Comment: 11 pages, 7 figure
Introducing one-shot work into fluctuation relations
Two approaches to small-scale and quantum thermodynamics are fluctuation
relations and one-shot statistical mechanics. Fluctuation relations (such as
Crooks' Theorem and Jarzynski's Equality) relate nonequilibrium behaviors to
equilibrium quantities such as free energy. One-shot statistical mechanics
involves statements about every run of an experiment, not just about averages
over trials.
We investigate the relation between the two approaches. We show that both
approaches feature the same notions of work and the same notions of probability
distributions over possible work values. The two approaches are alternative
toolkits with which to analyze these distributions. To combine the toolkits, we
show how one-shot work quantities can be defined and bounded in contexts
governed by Crooks' Theorem. These bounds provide a new bridge from one-shot
theory to experiments originally designed for testing fluctuation theorems.Comment: 37 pages, 6 figure
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