Minimal ancilla mediated quantum computation

Proctor, Timothy; Kendon, Viv

doi:10.1140/epjqt13

Cited by 4 publications

(11 citation statements)

References 44 publications

(75 reference statements)

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“…The schemes to reduce the number of operations required for a particular gate sequence, such as those given in Eqs. (13) and (14), require that more than two register qubits are entangled with the bus at the same time, and in particular more than one qubit is entangled with each quadrature of the bus. In order to create a closed phase space path via displacements on a spin coherent state, it is necessary to take into account the curvature of the phase space as quantified by Eq.…”

Section: B the Computational Modelmentioning

confidence: 99%

Quantum computation mediated by ancillary qudits and spin coherent states

2015

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Publisher's copyright statement:Reprinted with permission from the American Physical Society: Physical Review A 91, 012308 c (2015) by the American Physical Society. Readers may view, browse, and/or download material for temporary copying purposes only, provided these uses are for noncommercial personal purposes. Except as provided by law, this material may not be further reproduced, distributed, transmitted, modied, adapted, performed, displayed, published, or sold in whole or part, without prior written permission from the American Physical Society.Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Models of universal quantum computation in which the required interactions between register (computational) qubits are mediated by some ancillary system are highly relevant to experimental realizations of a quantum computer. We introduce such a universal model that employs a d-dimensional ancillary qudit. The ancilla-register interactions take the form of controlled displacements operators, with a displacement operator defined on the periodic and discrete lattice phase space of a qudit. We show that these interactions can implement controlled phase gates on the register by utilizing geometric phases that are created when closed loops are traversed in this phase space. The extra degrees of freedom of the ancilla can be harnessed to reduce the number of operations required for certain gate sequences. In particular, we see that the computational advantages of the quantum bus (qubus) architecture, which employs a field-mode ancilla, are also applicable to this model. We then explore an alternative ancilla-mediated model which employs a spin ensemble as the ancillary system and again the interactions with the register qubits are via controlled displacement operators, with a displacement operator defined on the Bloch sphere phase space of the spin coherent states of the ensemble. We discuss the computational advantages of this model and its relationship with the qubus architecture.

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Section: B the Computational Modelmentioning

confidence: 99%

Quantum computation mediated by ancillary qudits and spin coherent states

2015

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“…This minimises the disturbance to the register qubits, preserving quantum coherence for longer. It is possible to minimise the interactions to the point where universal quantum computation can be performed by a sequence of ancillaregister interactions plus preparation of the ancillas in different computational basis states [51,96].…”

Section: Discussionmentioning

confidence: 99%

“…The gate method for local gate on the register with the swap-type interaction described above has reverted to using unitary local controls (here of the ancilla). If we do not wish to rely on such controls, then with a minor adaption to the interaction it is possible to replace them with ancilla preparation in the different computational basis states, which then determines which local gates are applied to the register subsystem [51,96]. For qubits, this is particularly simple: by appending an additional (fixed) local u gate on the ancilla to the interaction (after swap · CR(θ)), April 4, 2016 0: 16 Contemporary Physics Hybrid˙quantum˙computing˙with˙ancillas two interactions of a register qubit with an ancilla in the state |0 or |1 respectively implement u and R(θ)uR(θ) on the register qubit respectively [96].…”

Section: Ancillamentioning

confidence: 99%

Hybrid quantum computing with ancillas

Proctor

Kendon

2016

Contemporary Physics

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In the quest to build a practical quantum computer, it is important to use efficient schemes for enacting the elementary quantum operations from which quantum computer programs are constructed. The opposing requirements of well-protected quantum data and fast quantum operations must be balanced to maintain the integrity of the quantum information throughout the computation. One important approach to quantum operations is to use an extra quantum system - an ancilla - to interact with the quantum data register. Ancillas can mediate interactions between separated quantum registers, and by using fresh ancillas for each quantum operation, data integrity can be preserved for longer. This review provides an overview of the basic concepts of the gate model quantum computer architecture, including the different possible forms of information encodings - from base two up to continuous variables - and a more detailed description of how the main types of ancilla-mediated quantum operations provide efficient quantum gates.Comment: Review paper. An introduction to quantum computation with qudits and continuous variables, and a review of ancilla-based gate method

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“…This model is applicable to all types of QVs, although it is perhaps better suited to qubits and qudits than QCVs, as discussed later, and it includes as a special case a qubit-based model presented by some of these authors in Ref. [36].…”

Section: Minimal-control Computationmentioning

confidence: 99%

“…However, if this model were to be of further interest (outside the qubit-based setting, in which further appropriate choices for u and φ can be found in [30,36]), it would be important to undertake a more thorough investigation of which parameter choices in the interaction are sufficient for universality. Finally, note that universality in the QCV model has not been investigated as it does not seem likely that this model will be of practical interest in this case.…”

Section: Appendix Bmentioning

confidence: 99%

Ancilla-driven quantum computation for qudits and continuous variables

et al. 2017

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(2017) 'Ancilla-driven quantum computation for qudits and continuous variables. ', Physical review A., 95 (5). 052317.Further information on publisher's website:https://doi.org/10.1103/PhysRevA.95.052317Publisher's copyright statement:Reprinted with permission from the American Physical Society: Physical Review A 95, 052317 c (2017) by the American Physical Society. Readers may view, browse, and/or download material for temporary copying purposes only, provided these uses are for noncommercial personal purposes. Except as provided by law, this material may not be further reproduced, distributed, transmitted, modied, adapted, performed, displayed, published, or sold in whole or part, without prior written permission from the American Physical Society.Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Although qubits are the leading candidate for the basic elements in a quantum computer, there are also a range of reasons to consider using higher-dimensional qudits or quantum continuous variables (QCVs). In this paper, we use a general "quantum variable" formalism to propose a method of quantum computation in which ancillas are used to mediate gates on a well-isolated "quantum memory" register and which may be applied to the setting of qubits, qudits (for d > 2), or QCVs. More specifically, we present a model in which universal quantum computation may be implemented on a register using only repeated applications of a single fixed two-body ancilla-register interaction gate, ancillas prepared in a single state, and local measurements of these ancillas. In order to maintain determinism in the computation, adaptive measurements via a classical feed forward of measurement outcomes are used, with the method similar to that in measurement-based quantum computation (MBQC). We show that our model has the same hybrid quantum-classical processing advantages as MBQC, including the power to implement any Clifford circuit in essentially one layer of quantum computation. In some physical settings, high-quality measurements of the ancillas may be highly challenging or not possible, and hence we also present a globally unitary model which replaces the need for measurements of the ancillas with the requirement for ancillas to be prepared in states from a fixed orthonormal basis. Finally, we discuss settings in which these models may be of practical interest.

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Minimal ancilla mediated quantum computation

Cited by 4 publications

References 44 publications

Quantum computation mediated by ancillary qudits and spin coherent states

Quantum computation mediated by ancillary qudits and spin coherent states

Hybrid quantum computing with ancillas

Ancilla-driven quantum computation for qudits and continuous variables

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