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In this paper we study a model of a Quantum Branching Program (QBP) and investigate its computational power. We prove a general lower bound on the width of read-once QBPs, which we show to be almost tight on certain symmetric function.

Quantum Physics · Physics 2007-05-23 Farid Ablayev , Aida Gainutdinova , Marek Karpinski

Computing the Jones polynomial of general link diagrams is known to be $\#$P-hard, while restricting the computation to braid closures on fixed number of strands allows for a polynomial time algorithm. We investigate polynomial time…

Geometric Topology · Mathematics 2026-01-06 Tuomas Kelomäki , Dirk Schütz

We study quantum communication protocols, in which the players' storage starts out in a state where one qubit is in a pure state, and all other qubits are totally mixed (i.e. in a random state), and no other storage is available (for…

Quantum Physics · Physics 2020-01-01 Hartmut Klauck , Debbie Lim

Two of the major obstacles to achieve quantum computing (QC) are (i) scalability to many qubits and (ii) controlled connectivity between any selected qubits. Using Josephson charge qubits, here we propose an experimentally realizable method…

Superconductivity · Physics 2007-05-23 J. Q. You , J. S. Tsai , Franco Nori

Topological quantum computing promises intrinsic fault tolerance by encoding quantum information in non-Abelian anyons, where quantum gates are implemented via braiding. While braiding operations are robust against local perturbations, a…

Quantum Physics · Physics 2025-08-15 Themba Hodge , Philipp Frey , Stephan Rachel

While building a universal quantum computer remains challenging, devices of restricted power such as the so-called one pure qubit model have attracted considerable attention. An important step in the construction of these limited quantum…

Quantum Physics · Physics 2014-03-10 Theodoros Kapourniotis , Elham Kashefi , Animesh Datta

Using a simple recurrence relation we give a new method to compute Jones polynomials of closed braids: we find a general expansion formula and a rational generating function for Jones polynomials. The method is used to estimate degree of…

Geometric Topology · Mathematics 2010-02-22 Barbu Berceanu , Abdul Rauf Nizami

In this paper, we study the problem of model-checking quantum pushdown systems from a computational complexity point of view. We arrive at the following equally important, interesting new results: We first extend the notions of the {\it…

Logic in Computer Science · Computer Science 2026-05-11 Deren Lin , Tianrong Lin

The complexity class $PSPACE$ includes all computational problems that can be solved by a classical computer with polynomial memory. All $PSPACE$ problems are known to be solvable by a quantum computer too with polynomial memory and are,…

Computational Complexity · Computer Science 2023-06-27 Shibdas Roy

In topologically-protected quantum computation, quantum gates can be carried out by adiabatically braiding two-dimensional quasiparticles, reminiscent of entangled world lines. Bonesteel et al. [Phys. Rev. Lett. 95, 140503 (2005)], as well…

Quantum Physics · Physics 2013-02-14 Ross B. McDonald , Helmut G. Katzgraber

Although quantum computers are capable of solving problems like factoring exponentially faster than the best-known classical algorithms, determining the resources responsible for their computational power remains unclear. An important class…

Quantum Physics · Physics 2016-05-11 Nana Liu , Jayne Thompson , Christian Weedbrook , Seth Lloyd , Vlatko Vedral , Mile Gu , Kavan Modi

Analysis and verification of quantum circuits are highly challenging, given the exponential dependence of the number of states on the number of qubits. For analytical derivation, we propose a new quantum polynomial representation (QPR) to…

Quantum Physics · Physics 2025-03-14 Yu-Ting Kao , Hao-Yu Lu , Yeong-Jar Chang , Darsen Lu

We study the computational complexity of certain integrable quantum theories in 1+1 dimensions. We formalize a model of quantum computation based on these theories. In this model, distinguishable particles start out with known momenta and…

Quantum Physics · Physics 2016-01-01 Saeed Mehraban

Deterministic quantum computation with one quantum bit (DQC1) is a model of quantum computing where the input restricted to containing a single qubit in a pure state and with all other qubits in a completely-mixed state, with only a single…

Quantum Physics · Physics 2015-03-02 Tomoyuki Morimae , Keisuke Fujii , Joseph F. Fitzsimons

We present a differentiable joint pruning and quantization (DJPQ) scheme. We frame neural network compression as a joint gradient-based optimization problem, trading off between model pruning and quantization automatically for hardware…

Machine Learning · Computer Science 2021-04-06 Ying Wang , Yadong Lu , Tijmen Blankevoort

A goal of quantum information technology is to control the quantum state of a system, including its preparation, manipulation, and measurement. However, scalability to many qubits and controlled connectivity between any selected qubits are…

Superconductivity · Physics 2009-11-10 J. Q. You , J. S. Tsai , Franco Nori

The exact cover problem is an NP-complete problem with broad applications. Studies show that although applying the Quantum Approximate Optimization Algorithm (QAOA) to this problem can yield improved solution quality with deeper circuit…

Quantum Physics · Physics 2025-09-16 Xiao-Hui Ni , Jia-Cheng Fan , Ling-Xiao Li , Zi-Wen Huang , Su-Juan Qin , Bing-Jie Xu , Wei-Huang , Fei Gao

To successfully execute large-scale algorithms, a quantum computer will need to perform its elementary operations near perfectly. This is a fundamental challenge since all physical qubits suffer a considerable level of noise. Moreover, real…

Quantum Physics · Physics 2023-06-29 Armands Strikis , Simon C. Benjamin , Benjamin J. Brown

Distinguishing logarithmic depth quantum circuits on mixed states is shown to be complete for QIP, the class of problems having quantum interactive proof systems. Circuits in this model can represent arbitrary quantum processes, and thus…

Quantum Physics · Physics 2010-06-02 Bill Rosgen

In a recent preprint by Deutsch et al. [1995] the authors suggest the possibility of polynomial approximability of arbitrary unitary operations on $n$ qubits by 2-qubit unitary operations. We address that comment by proving strong lower…

Quantum Physics · Physics 2008-02-03 E. Knill