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We define formally decohered quantum computers (using density matrices), and present a simulation of them by a probabalistic classical Turing Machine. We study the slowdown of the simulation for two cases: (1) sequential quantum computers,…

Quantum Physics · Physics 2007-05-23 Dorit Aharonov , Michael Ben-Or

A denotational semantics of quantum Turing machines having a quantum control is defined in the dagger compact closed category of finite dimensional Hilbert spaces. Using the Moore-Penrose generalized inverse, a new additive trace is…

Quantum Physics · Physics 2014-04-02 Miklós Bartha

Quantum computers promise to perform computations beyond the reach of modern computers with profound implications for scientific research. Due to remarkable technological advances, small scale devices are now becoming available for use. One…

Strongly Correlated Electrons · Physics 2022-05-20 Adam Smith , Bernhard Jobst , Andrew G. Green , Frank Pollmann

Metastability is a spurious mode of operation in digital signals, where an electrical signal fails to settle into a stable state within a specified time, leading to uncertainty and potentially failing downstream hardware. A system that…

Computational Complexity · Computer Science 2026-04-21 Johannes Bund , Amir Leshem , Moti Medina

In this paper, we introduce classically time-controlled quantum automata or CTQA, which is a reasonable modification of Moore-Crutchfield quantum finite automata that uses time-dependent evolution and a "scheduler" defining how long each…

Formal Languages and Automata Theory · Computer Science 2025-09-25 Alejandro Díaz-Caro , Marcos Villagra

Despite the fact that a complete theoretical description of critical phenomena in connection with phase transitions has been well-established through the renormalization group theory, the microscopic nature of the phase transitions remains…

Statistical Mechanics · Physics 2025-11-07 Yun-Tong Yang , Fu-Zhou Chen , Hong-Gang Luo

Recently, among experiments for realization of quantum computers, NMR quantum computers have achieved the most impressive succession. There is a model of the NMR quantum computation,namely Atsumi and Nishino's bulk quantum Turing Machine.…

Computational Complexity · Computer Science 2007-05-23 Tetsushi Matsui

The rapid evolution of artificial intelligence has driven interest in Long Short-Term Memory (LSTM) networks for their effectiveness in processing sequential data. However, traditional LSTMs are limited by issues such as the vanishing…

Quantum Physics · Physics 2024-08-27 Yifan Zhou , Chong Cheng Xu , Mingi Song , Yew Kee Wong , Kangsong Du

We consider the Rabi Hamiltonian which exhibits a quantum phase transition (QPT) despite consisting only of a single-mode cavity field and a two-level atom. We prove QPT by deriving an exact solution in the limit where the atomic transition…

Quantum Physics · Physics 2015-10-30 Myung-Joong Hwang , Ricardo Puebla , Martin B. Plenio

A universal quantum computing scheme, with a universal set of logical gates, is proposed based on networks of 1D quantum systems. The encoding of information is in terms of universal features of gapped phases, for which effective field…

Quantum Physics · Physics 2019-07-24 Dong-Sheng Wang

Quantum state tomography via local measurements is an efficient tool for characterizing quantum states. However it requires that the original global state be uniquely determined (UD) by its local reduced density matrices (RDMs). In this…

Random access machines (RAMs) and random access stored-program machines (RASPs) are models of computing that are closer to the architecture of real-world computers than Turing machines (TMs). They are also convenient in complexity analysis…

Logic in Computer Science · Computer Science 2022-09-13 Qisheng Wang , Mingsheng Ying

Quantum state tomography aims to estimate the state of a quantum mechanical system which is described by a trace one, Hermitian positive semidefinite complex matrix, given a set of measurements of the state. Existing works focus on…

Quantum Physics · Physics 2023-03-22 Siva Shanmugam , Sheetal Kalyani

This work introduces a relative diffusion transformation (RDT) - a simple unitary transformation which acts in a subspace, localized by an oracle. Such a transformation can not be fulfilled on quantum Turing machines with this oracle in…

Quantum Physics · Physics 2008-02-03 Yuri Ozhigov

Squeezing transformation as an essential component, gives rise to the possibility to perform various tasks of quantum information processing. However, the reported squeezing gate with best performance so far is a conditional realization at…

Quantum Physics · Physics 2022-02-16 Xiaocong Sun , Yajun Wang , Yuhang Tian , Qingwei Wang , Long Tian , Yaohui Zheng , Kunchi Peng

For the additive real BSS machines using only constants 0 and 1 and order tests we consider the corresponding Turing reducibility and characterize some semi-decidable decision problems over the reals. In order to refine, step-by-step, a…

Logic in Computer Science · Computer Science 2016-03-27 Christine Gaßner

This is a comprehensive review on fault-tolerant topological quantum computation with the surface codes. The basic concepts and useful tools underlying fault-tolerant quantum computation, such as universal quantum computation, stabilizer…

Quantum Physics · Physics 2015-04-08 Keisuke Fujii

According to the statistical interpretation of quantum theory, quantum computers form a distinguished class of probabilistic machines (PMs) by encoding n qubits in 2n pbits (random binary variables). This raises the possibility of a…

Quantum Physics · Physics 2007-05-23 P. Gralewicz

We investigate quantum phase transitions (QPTs) in spin chain systems characterized by local Hamiltonians with matrix product ground states. We show how to theoretically engineer such QPT points between states with predetermined properties.…

Statistical Mechanics · Physics 2009-11-11 Michael M. Wolf , Gerardo Ortiz , Frank Verstraete , J. Ignacio Cirac

Continuous-variable cluster states offer a potentially promising method of implementing a quantum computer. This paper extends and further refines theoretical foundations and protocols for experimental implementation. We give a…

Quantum Physics · Physics 2015-05-13 Mile Gu , Christian Weedbrook , Nicolas C. Menicucci , Timothy C. Ralph , Peter van Loock
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