Classically controlled quantum computation

Abstract : It is reasonable to assume that quantum computations take place under the control of the classical world. For modelling this standard situation, we introduce a Classically controlled Quantum Turing Machine (CQTM), which is a Turing machine with a quantum tape for acting on quantum data, and a classical transition function for formalised classical control. In a CQTM, unitary transformations and quantum measurements are allowed. We show that any classical Turing machine can be simulated by a CQTM without loss of efficiency. Furthermore, we show that any $k$-tape CQTM can be simulated by a 2-tape CQTM with a quadratic loss of efficiency. In order to compare CQTMs with existing models of quantum computation, we prove that any uniform family of quantum circuits (Yao 1993) is efficiently approximated by a CQTM. Moreover, we prove that any semi-uniform family of quantum circuits (Nishimura and Ozawa 2002), and any measurement calculus pattern (Danos et al. 2004) are efficiently simulated by a CQTM. Finally, we introduce a Measurement-based Quantum Turing Machine (MQTM), which is a restriction of CQTMs in which only projective measurements are allowed. We prove that any CQTM is efficiently simulated by a MQTM. In order to appreciate the similarity between programming classical Turing machines and programming CQTMs, some examples of CQTMs are given.
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Journal articles
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https://hal.archives-ouvertes.fr/hal-01378709
Contributor : Simon Perdrix <>
Submitted on : Monday, October 10, 2016 - 4:29:53 PM
Last modification on : Thursday, January 11, 2018 - 6:27:34 AM

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Simon Perdrix, Philippe Jorrand. Classically controlled quantum computation. Mathematical Structures in Computer Science, Cambridge University Press (CUP), 2006, 16 (04), ⟨10.1017/S096012950600538X⟩. ⟨hal-01378709⟩

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