454 research outputs found
Equivalence Checking of Sequential Quantum Circuits
We define a formal framework for equivalence checking of sequential quantum
circuits. The model we adopted is a quantum state machine, which is a natural
quantum generalisation of Mealy machines. A major difficulty in checking
quantum circuits (but not present in checking classical circuits) is that the
state spaces of quantum circuits are continuums. This difficulty is resolved by
our main theorem showing that equivalence checking of two quantum Mealy
machines can be done with input sequences that are taken from some chosen basis
(which are finite) and have a length quadratic in the dimensions of the state
Hilbert spaces of the machines. Based on this theoretical result, we develop an
(and to the best of our knowledge, the first) algorithm for checking
equivalence of sequential quantum circuits. A case study and experiments are
presented
Sync+Sync: A Covert Channel Built on fsync with Storage
Scientists have built a variety of covert channels for secretive information
transmission with CPU cache and main memory. In this paper, we turn to a lower
level in the memory hierarchy, i.e., persistent storage. Most programs store
intermediate or eventual results in the form of files and some of them call
fsync to synchronously persist a file with storage device for orderly
persistence. Our quantitative study shows that one program would undergo
significantly longer response time for fsync call if the other program is
concurrently calling fsync, although they do not share any data. We further
find that, concurrent fsync calls contend at multiple levels of storage stack
due to sharing software structures (e.g., Ext4's journal) and hardware
resources (e.g., disk's I/O dispatch queue).
We accordingly build a covert channel named Sync+Sync. Sync+Sync delivers a
transmission bandwidth of 20,000 bits per second at an error rate of about
0.40% with an ordinary solid-state drive. Sync+Sync can be conducted in
cross-disk partition, cross-file system, cross-container, cross-virtual
machine, and even cross-disk drive fashions, without sharing data between
programs. Next, we launch side-channel attacks with Sync+Sync and manage to
precisely detect operations of a victim database (e.g., insert/update and
B-Tree node split). We also leverage Sync+Sync to distinguish applications and
websites with high accuracy by detecting and analyzing their fsync frequencies
and flushed data volumes. These attacks are useful to support further
fine-grained information leakage.Comment: A full version for the paper with the same title accepted by the 33rd
USENIX Security Symposium (USENIX Security 2024
Fast Quantum Algorithms for Trace Distance Estimation
In quantum information, trace distance is a basic metric of
distinguishability between quantum states. However, there is no known efficient
approach to estimate the value of trace distance in general. In this paper, we
propose efficient quantum algorithms for estimating the trace distance within
additive error between mixed quantum states of rank .
Specifically, we first provide a quantum algorithm using queries to the quantum circuits that prepare the
purifications of quantum states. Then, we modify this quantum algorithm to
obtain another algorithm using samples of
quantum states, which can be applied to quantum state certification. These
algorithms have query/sample complexities that are independent of the dimension
of quantum states, and their time complexities only incur an extra factor. In addition, we show that the decision version of low-rank trace
distance estimation is -complete.Comment: Final version. Improve proof details, add BQP-completeness. 31 pages,
2 algorithms, 2 tables, 2 figure
Oscillation and asymptotic behavior for a class of delay parabolic differential
AbstractSome comparative theorems are given for the oscillation and asymptotic behavior for a class of high order delay parabolic differential equations of the form ∂n(u(x,t)−p(t)u(x,t−τ))∂tn−a(t)△u+c(x,t,u)+∫abq(x,t,ξ)f(u(x,g1(t,ξ)),…,u(x,gl(t,ξ)))dσ(ξ)=0,(x,t)∈Ω×R+≡G, where n is an odd integer, Ω is a bounded domain in Rm with a smooth boundary ∂Ω, and △ is the Laplacian operation with three boundary value conditions. Our results extend some of those of [P. Wang, Oscillatory criteria of nonlinear hyperbolic equations with continuous deviating arguments, Appl. Math. Comput. 106 (1999), 163–169] substantially
Calliffusion: Chinese Calligraphy Generation and Style Transfer with Diffusion Modeling
In this paper, we propose Calliffusion, a system for generating high-quality
Chinese calligraphy using diffusion models. Our model architecture is based on
DDPM (Denoising Diffusion Probabilistic Models), and it is capable of
generating common characters in five different scripts and mimicking the styles
of famous calligraphers. Experiments demonstrate that our model can generate
calligraphy that is difficult to distinguish from real artworks and that our
controls for characters, scripts, and styles are effective. Moreover, we
demonstrate one-shot transfer learning, using LoRA (Low-Rank Adaptation) to
transfer Chinese calligraphy art styles to unseen characters and even
out-of-domain symbols such as English letters and digits.Comment: 5pages, International Conference on Computational Creativity, ICC
Succinct quantum testers for closeness and -wise uniformity of probability distributions
We explore potential quantum speedups for the fundamental problem of testing
the properties of closeness and -wise uniformity of probability
distributions.
\textit{Closeness testing} is the problem of distinguishing whether two
-dimensional distributions are identical or at least -far in
- or -distance. We show that the quantum query complexities for
- and -closeness testing are O\rbra{\sqrt{n}/\varepsilon} and
O\rbra{1/\varepsilon}, respectively, both of which achieve optimal dependence
on , improving the prior best results of
\hyperlink{cite.gilyen2019distributional}{Gily{\'e}n and Li~(2019)}.
\textit{-wise uniformity testing} is the problem of distinguishing whether
a distribution over \cbra{0, 1}^n is uniform when restricted to any
coordinates or -far from any such distributions. We propose the
first quantum algorithm for this problem with query complexity
O\rbra{\sqrt{n^k}/\varepsilon}, achieving a quadratic speedup over the
state-of-the-art classical algorithm with sample complexity
O\rbra{n^k/\varepsilon^2} by \hyperlink{cite.o2018closeness}{O'Donnell and
Zhao (2018)}. Moreover, when our quantum algorithm outperforms any
classical one because of the classical lower bound
\Omega\rbra{n/\varepsilon^2}.
All our quantum algorithms are fairly simple and time-efficient, using only
basic quantum subroutines such as amplitude estimation.Comment: We have added the proof of lower bounds and have polished the
languag
Parallel Quantum Algorithm for Hamiltonian Simulation
We study how parallelism can speed up quantum simulation. A parallel quantum
algorithm is proposed for simulating the dynamics of a large class of
Hamiltonians with good sparse structures, called uniform-structured
Hamiltonians, including various Hamiltonians of practical interest like local
Hamiltonians and Pauli sums. Given the oracle access to the target sparse
Hamiltonian, in both query and gate complexity, the running time of our
parallel quantum simulation algorithm measured by the quantum circuit depth has
a doubly (poly-)logarithmic dependence
on the simulation precision . This presents an exponential
improvement over the dependence of
previous optimal sparse Hamiltonian simulation algorithm without parallelism.
To obtain this result, we introduce a novel notion of parallel quantum walk,
based on Childs' quantum walk. The target evolution unitary is approximated by
a truncated Taylor series, which is obtained by combining these quantum walks
in a parallel way. A lower bound is
established, showing that the -dependence of the gate depth achieved
in this work cannot be significantly improved.
Our algorithm is applied to simulating three physical models: the Heisenberg
model, the Sachdev-Ye-Kitaev model and a quantum chemistry model in second
quantization. By explicitly calculating the gate complexity for implementing
the oracles, we show that on all these models, the total gate depth of our
algorithm has a dependence in the
parallel setting.Comment: Minor revision. 55 pages, 6 figures, 1 tabl
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