Functional quantum computing: An optical approach

Rambo, Timothy M.; Altepeter, Joseph B.; Kumar, Prem; D’Ariano, Giacomo Mauro

doi:10.1103/physreva.93.052321

Cited by 26 publications

(26 citation statements)

References 29 publications

(40 reference statements)

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“…We illustrate how this additional knowledge can significantly change what can be made modular. We connect our results to existing studies on controlling an unknown unitary on a quantum degree of freedom [14][15][16][17][18]. We illustrate that the diversity of conclusions about whether this is possible naturally emerges from different implicit assumptions about how the unknown unitary is physically realized.…”

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confidence: 60%

Quantum plug n’ play: modular computation in the quantum regime

et al. 2018

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Classical computation is modular. It exploits plug n' play architectures which allow us to use prefabricated circuits without knowing their construction. This bestows advantages such as allowing parts of the computational process to be outsourced, and permitting individual circuit components to be exchanged and upgraded. Here, we introduce a formal framework to describe modularity in the quantum regime. We demonstrate a 'no-go' theorem, stipulating that it is not always possible to make use of quantum circuits without knowing their construction. This has significant consequences for quantum algorithms, forcing the circuit implementation of certain quantum algorithms to be rebuilt almost entirely from scratch after incremental changes in the problem-such as changing the number being factored in Shor's algorithm. We develop a workaround capable of restoring modularity, and apply it to design a modular version of Shor's algorithm that exhibits increased versatility and reduced complexity. In doing so we pave the way to a realistic framework whereby 'quantum chips' and remote servers can be invoked (or assembled) to implement various parts of a more complex quantum computation.repository of external servers, each specialized in executing specific quantum algorithms on supplied input. To what extent can a client, Alice, construct a universal device that invokes such a server -much as one invokes built-in functions on Mathematica-such that her device automatically performs a computation [ ] U , whenever the server's algorithm transforms an input fñThis question is particularly important for a prominent class of quantum algorithms that encompasses quantum factoring, solution of linear equations, and the DQC1 (the power of one bit of quantum information) algorithm for evaluating the normalized trace of unitary matrices [4][5][6][7][8][9][10][11]. These algorithms share the common property that their classical input x is encoded within a suitable unitary operator U x . Quantum speed-up explicitly exploits the property that U x can scale exponentially, and yet still be represented by a polynomial sized quantum circuit. The algorithm then operates by realizing some U x -dependent complex quantum process [ ] U x , whose output statistics compute some desired function f (x).Modularity is naturally desirable as each input x requires a different operator U x . A naive synthesis of [ ] U x would involve creating a different quantum circuit for each possible input which is far from ideal. Could Alice adopt a more modular approach? One may envision a series of different black-boxes, each promising to output fñ | U when given input fñ | . Can Alice then construct some fixed 'plug n' play device', such that by 'plugging in' a black-box that implements a specific U x , her device computes [ ] U x (see figure 1)? If possible, such a device is clearly advantageous. Different laboratories could engineer implementations of different U x that exploit the advantages of specific physical realizations; which can then be interchanged free...

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confidence: 60%

Quantum plug n’ play: modular computation in the quantum regime

et al. 2018

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“…Recognizing causality as a postulate for the theory has allowed us for the first time to consider variations of the theory that do not satisfy it. This has spawned a full research line about non-causal variations of quantum theory, ranging from the theory of quantum combs [21] (which still has an interpretation in terms of an underlying causal theory) to theories with dynamical causal ordering [22][23][24][25], and experimental tests have been also devised [26,27].…”

Section: (F) From Cinderella To Principle Of Physicsmentioning

confidence: 99%

Causality re-established

D’Ariano

2018

Phil. Trans. R. Soc. A.

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Causality has never gained the status of a 'law' or 'principle' in physics. Some recent literature has even popularized the false idea that causality is a notion that should be banned from theory. Such misconception relies on an alleged universality of the reversibility of the laws of physics, based either on the determinism of classical theory, or on the multiverse interpretation of quantum theory, in both cases motivated by mere interpretational requirements for realism of the theory. Here, I will show that a properly defined unambiguous notion of causality is a theorem of quantum theory, which is also a falsifiable proposition of the theory. Such a notion of causality appeared in the literature within the framework of operational probabilistic theories. It is a genuinely theoretical notion, corresponding to establishing a definite partial order among events, in the same way as we do by using the future causal cone on Minkowski space. The notion of causality is logically completely independent of the misidentified concept of 'determinism', and, being a consequence of quantum theory, is ubiquitous in physics. In addition, as classical theory can be regarded as a restriction of quantum theory, causality holds also in the classical case, although the determinism of the theory trivializes it. I then conclude by arguing that causality naturally establishes an arrow of time. This implies that the scenario of the 'block Universe' and the connected 'past hypothesis' are incompatible with causality, and thus with quantum theory: they are both doomed to remain mere interpretations and, as such, are not falsifiable, similar to the hypothesis of 'super-determinism'.This article is part of a discussion meeting issue 'Foundations of quantum mechanics and their impact on contemporary society'.

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“…Fortunately, the suitable ultrafast optical switching device, that enables us to route single photons for quantum information processing, has been demonstrated. These switches exhibit a minimal loss, high speed performance, and a high contrast without disturbing the quantum state of photons that pass through them [80][81][82]. For instance, an ultrafast switch has been experimentally demonstrated and it completes the switch operation in 10ps [80], which is much shorter than the electron spin coherence time of a charged QD (3µs) [60,61].…”

Section: Discussion and Summarymentioning

confidence: 99%

Self-error-corrected hyperparallel photonic quantum computation working with both the polarization and the spatial-mode degrees of freedom

Wang

et al. 2018

Opt. Express

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Usually, the hyperparallel quantum computation can speed up quantum computing, reduce the quantum resource consumed largely, resist to noise, and simplify the storage of quantum information. Here, we present the first scheme for the self-error-corrected hyperparallel photonic quantum computation working with both the polarization and the spatial-mode degrees of freedom of photon systems simultaneously. It can prevent bit-flip errors from happening with an imperfect nonlinear interaction in the nearly realistic condition. We give the way to design the universal hyperparallel photonic quantum controlled-NOT (CNOT) gate on a two-photon system, resorting to the nonlinear interaction between the circularly polarized photon and the electron spin in the quantum dot in a double-sided microcavity system, by taking the imperfect interaction in the nearly realistic condition into account. Its self-error-corrected pattern prevents the bit-flip errors from happening in the hyperparallel quantum CNOT gate, guarantees the robust fidelity, and relaxes the requirement for its experiment. Meanwhile, this scheme works in a failure-heralded way. Also, we generalize this approach to achieve the self-error-corrected hyperparallel quantum CNOTN gate working on a multiple-photon system. These good features make this scheme more useful in the photonic quantum computation and quantum communication in the future.

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Functional quantum computing: An optical approach

Cited by 26 publications

References 29 publications

Quantum plug n’ play: modular computation in the quantum regime

Quantum plug n’ play: modular computation in the quantum regime

Causality re-established

Self-error-corrected hyperparallel photonic quantum computation working with both the polarization and the spatial-mode degrees of freedom

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