893 research outputs found
Chaotic Compilation for Encrypted Computing: Obfuscation but Not in Name
An `obfuscation' for encrypted computing is quantified exactly here, leading
to an argument that security against polynomial-time attacks has been achieved
for user data via the deliberately `chaotic' compilation required for security
properties in that environment. Encrypted computing is the emerging science and
technology of processors that take encrypted inputs to encrypted outputs via
encrypted intermediate values (at nearly conventional speeds). The aim is to
make user data in general-purpose computing secure against the operator and
operating system as potential adversaries. A stumbling block has always been
that memory addresses are data and good encryption means the encrypted value
varies randomly, and that makes hitting any target in memory problematic
without address decryption, yet decryption anywhere on the memory path would
open up many easily exploitable vulnerabilities. This paper `solves (chaotic)
compilation' for processors without address decryption, covering all of ANSI C
while satisfying the required security properties and opening up the field for
the standard software tool-chain and infrastructure. That produces the argument
referred to above, which may also hold without encryption.Comment: 31 pages. Version update adds "Chaotic" in title and throughout
paper, and recasts abstract and Intro and other sections of the text for
better access by cryptologists. To the same end it introduces the polynomial
time defense argument explicitly in the final section, having now set that
denouement out in the abstract and intr
The non-Markovian quantum behavior of open systems: An exact Monte Carlo method employing stochastic product states
It is shown that the exact dynamics of a composite quantum system can be
represented through a pair of product states which evolve according to a
Markovian random jump process. This representation is used to design a general
Monte Carlo wave function method that enables the stochastic treatment of the
full non-Markovian behavior of open quantum systems. Numerical simulations are
carried out which demonstrate that the method is applicable to open systems
strongly coupled to a bosonic reservoir, as well as to the interaction with a
spin bath. Full details of the simulation algorithms are given, together with
an investigation of the dynamics of fluctuations. Several potential
generalizations of the method are outlined.Comment: 14 pages, 5 figure
Quantum jumps and entropy production
The irreversible motion of an open quantum system can be represented through
an ensemble of state vectors following a stochastic dynamics with piecewise
deterministic paths. It is shown that this representation leads to a natural
definition of the rate of quantum entropy production. The entropy production
rate is expressed in terms of the von Neumann entropy and of the numbers of
quantum jumps corresponding to the various decay channels of the open system.
The proof of the positivity and of the convexity of the entropy production rate
is given. Monte Carlo simulations of the stochastic dynamics of a driven qubit
and of a -configuration involving a dark state are performed in order
to illustrate the general theory.Comment: 7 pages, 2 figure
A First Practical Fully Homomorphic Crypto-Processor Design: The Secret Computer is Nearly Here
Following a sequence of hardware designs for a fully homomorphic
crypto-processor - a general purpose processor that natively runs encrypted
machine code on encrypted data in registers and memory, resulting in encrypted
machine states - proposed by the authors in 2014, we discuss a working
prototype of the first of those, a so-called `pseudo-homomorphic' design. This
processor is in principle safe against physical or software-based attacks by
the owner/operator of the processor on user processes running in it. The
processor is intended as a more secure option for those emerging computing
paradigms that require trust to be placed in computations carried out in remote
locations or overseen by untrusted operators.
The prototype has a single-pipeline superscalar architecture that runs
OpenRISC standard machine code in two distinct modes. The processor runs in the
encrypted mode (the unprivileged, `user' mode, with a long pipeline) at 60-70%
of the speed in the unencrypted mode (the privileged, `supervisor' mode, with a
short pipeline), emitting a completed encrypted instruction every 1.67-1.8
cycles on average in real trials.Comment: 6 pages, draf
Laser-based acceleration of non-relativistic electrons at a dielectric structure
A proof-of-principle experiment demonstrating dielectric laser acceleration
of non-relativistic electrons in the vicinity of a fused-silica grating is
reported. The grating structure is utilized to generate an electromagnetic
surface wave that travels synchronously with and efficiently imparts momentum
on 28keV electrons. We observe a maximum acceleration gradient of 25MeV/m. We
investigate in detail the parameter dependencies and find excellent agreement
with numerical simulations. With the availability of compact and efficient
fiber laser technology, these findings may pave the way towards an all-optical
compact particle accelerator. This work also represents the demonstration of
the inverse Smith-Purcell effect in the optical regime.Comment: 5 pages, 4 figure
Stochastic analysis and simulation of spin star systems
We discuss two methods of an exact stochastic representation of the
non-Markovian quantum dynamics of open systems. The first method employs a pair
of stochastic product vectors in the total system's state space, while the
second method uses a pair of state vectors in the open system's state space and
a random operator acting on the state space of the environment. Both techniques
lead to an exact solution of the von Neumann equation for the density matrix of
the total system. Employing a spin star model describing a central spin coupled
to bath of surrounding spins, we perform Monte Carlo simulations for both
variants of the stochastic dynamics. In addition, we derive analytical
expression for the expectation values of the stochastic dynamics to obtain the
exact solution for the density matrix of the central spin.Comment: 8 pages, 2 figure
Quantum Semi-Markov Processes
We construct a large class of non-Markovian master equations that describe
the dynamics of open quantum systems featuring strong memory effects, which
relies on a quantum generalization of the concept of classical semi-Markov
processes. General conditions for the complete positivity of the corresponding
quantum dynamical maps are formulated. The resulting non-Markovian quantum
processes allow the treatment of a variety of physical systems, as is
illustrated by means of various examples and applications, including quantum
optical systems and models of quantum transport.Comment: 4 pages, revtex, no figures, to appear in Phys. Rev. Let
Revealing correlations between a system and an inaccessible environment
How can we detect that our local, controllable quantum system is correlated
with some other inaccessible environmental system? The local detection method
developed in recent years allows to realize a dynamical witness for
correlations without requiring knowledge of or access to the environment that
is correlated with the local accessible quantum system. Here, we provide a
brief summary of the theoretical method and recent experimental studies with
single photons and trapped ions coupled to increasingly complex environments.Comment: 12 pages, 3 figure
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