46 research outputs found
Quantum Algorithms for Identifying Hidden Strings with Applications to Matroid Problems
In this paper, we explore quantum speedups for the problem, inspired by
matroid theory, of identifying a pair of -bit binary strings that are
promised to have the same number of 1s and differ in exactly two bits, by using
the max inner product oracle and the sub-set oracle. More specifically, given
two string satisfying the above constraints, for any
the max inner product oracle returns the max
value between and , and the sub-set oracle
indicates whether the index set of the 1s in is a subset of that in or
. We present a quantum algorithm consuming queries to the max inner
product oracle for identifying the pair , and prove that any
classical algorithm requires queries. Also, we present a
quantum algorithm consuming queries to the subset
oracle, and prove that any classical algorithm requires at least
queries. Therefore, quantum speedups are revealed in the two oracle models.
Furthermore, the above results are applied to the problem in matroid theory of
finding all the bases of a 2-bases matroid, where a matroid is called -bases
if it has bases
Compressibility-Aware Quantum Algorithms on Strings
Sublinear time quantum algorithms have been established for many fundamental
problems on strings. This work demonstrates that new, faster quantum algorithms
can be designed when the string is highly compressible. We focus on two popular
and theoretically significant compression algorithms -- the Lempel-Ziv77
algorithm (LZ77) and the Run-length-encoded Burrows-Wheeler Transform (RL-BWT),
and obtain the results below.
We first provide a quantum algorithm running in time
for finding the LZ77 factorization of an input string with
factors. Combined with multiple existing results, this yields an
time quantum algorithm for finding the RL-BWT encoding
with BWT runs. Note that . We complement these
results with lower bounds proving that our algorithms are optimal (up to
polylog factors).
Next, we study the problem of compressed indexing, where we provide a
time quantum algorithm for constructing a recently
designed space structure with equivalent capabilities as the
suffix tree. This data structure is then applied to numerous problems to obtain
sublinear time quantum algorithms when the input is highly compressible. For
example, we show that the longest common substring of two strings of total
length can be computed in time, where is the
number of factors in the LZ77 factorization of their concatenation. This beats
the best known time quantum algorithm when is
sufficiently small
High Performance Computing for DNA Sequence Alignment and Assembly
Recent advances in DNA sequencing technology have dramatically increased the scale and scope of DNA sequencing. These data are used for a wide variety of important biological analyzes, including genome sequencing, comparative genomics, transcriptome analysis, and personalized medicine but are complicated by the volume and complexity of the data involved. Given the massive size of these datasets, computational biology must draw on the advances of high performance computing.
Two fundamental computations in computational biology are read alignment and genome assembly. Read alignment maps short DNA sequences to a reference genome to discover conserved and polymorphic regions of the genome. Genome assembly computes the sequence of a genome from many short DNA sequences. Both computations benefit from recent advances in high performance computing to efficiently process the huge datasets involved, including using highly parallel graphics processing units (GPUs) as high performance desktop processors, and using the MapReduce framework coupled with cloud computing to parallelize computation to large compute grids. This dissertation demonstrates how these technologies can be used to accelerate these computations by orders of magnitude, and have the potential to make otherwise infeasible computations practical
Proceedings of the 26th International Symposium on Theoretical Aspects of Computer Science (STACS'09)
The Symposium on Theoretical Aspects of Computer Science (STACS) is held alternately in France and in Germany. The conference of February 26-28, 2009, held in Freiburg, is the 26th in this series. Previous meetings took place in Paris (1984), Saarbr¨ucken (1985), Orsay (1986), Passau (1987), Bordeaux (1988), Paderborn (1989), Rouen (1990), Hamburg (1991), Cachan (1992), W¨urzburg (1993), Caen (1994), M¨unchen (1995), Grenoble (1996), L¨ubeck (1997), Paris (1998), Trier (1999), Lille (2000), Dresden (2001), Antibes (2002), Berlin (2003), Montpellier (2004), Stuttgart (2005), Marseille (2006), Aachen (2007), and Bordeaux (2008). ..
Initial state preparation for quantum chemistry on quantum computers
Quantum algorithms for ground-state energy estimation of chemical systems
require a high-quality initial state. However, initial state preparation is
commonly either neglected entirely, or assumed to be solved by a simple product
state like Hartree-Fock. Even if a nontrivial state is prepared, strong
correlations render ground state overlap inadequate for quality assessment. In
this work, we address the initial state preparation problem with an end-to-end
algorithm that prepares and quantifies the quality of initial states,
accomplishing the latter with a new metric -- the energy distribution. To be
able to prepare more complicated initial states, we introduce an implementation
technique for states in the form of a sum of Slater determinants that exhibits
significantly better scaling than all prior approaches. We also propose
low-precision quantum phase estimation (QPE) for further state quality
refinement. The complete algorithm is capable of generating high-quality states
for energy estimation, and is shown in select cases to lower the overall
estimation cost by several orders of magnitude when compared with the best
single product state ansatz. More broadly, the energy distribution picture
suggests that the goal of QPE should be reinterpreted as generating
improvements compared to the energy of the initial state and other classical
estimates, which can still be achieved even if QPE does not project directly
onto the ground state. Finally, we show how the energy distribution can help in
identifying potential quantum advantage