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Why I am optimistic about the silicon-photonic route to quantum computing

Terry Rudolph

This is a short overview explaining how building a large-scale, silicon-photonic quantum computer has been reduced to the creation of good sources of 3-photon entangled states (and may simplify further). Given such sources, each photon needs to pass through a small, constant, number of components, interfering with at most 2 other spatially nearby photons, and current photonics engineering has already demonstrated the manufacture of thousands of components on two-dimensional semiconductor chips with performance that, once scaled up, allows the creation of tens of thousands of photons entangled in a state universal for quantum computation. At present the fully integrated, silicon-photonic architecture we envisage involves creating the required entangled states by starting with single-photons produced non-deterministically by pumping silicon waveguides (or cavities) combined with on-chip filters and nanowire superconducting detectors to herald that a photon has been produced. These sources are multiplexed into being near-deterministic, and the single photons then passed through an interferometer to non-deterministically produce small entangled states—necessarily multiplexed to near-determinism again. This is followed by a “ballistic” scattering of the small-scale entangled photons through an interferometer such that some photons are detected, leaving the remainder in a large-scale entangled state which is provably universal for quantum computing implemented by single-photon measurements. There are a large number of questions regarding the optimum ways to make and use the final cluster state, dealing with static imperfections, constructing the initial entangled photon sources and so on, that need to be investigated before we can aim for millions of qubits capable of billions of computational time steps. The focus in this article is on the theoretical side of such questions.


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The Maryland CS department is hiring new faculty this year, with multiple positions available in multiple areas. U. Maryland anticipates hiring in quantum information as part of this search. For further details and how to apply see:

http://www.cs.umd.edu/job/2016/104991-tenure-track-faculty-all-levels-and-paul-chrisman-iribe-chair-professorship

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The Joint Center for Quantum Information and Computer Science (QuICS) (http://www.quics.umd.edu) is seeking exceptional candidates for the QuICS Hartree Postdoctoral Fellowships in Quantum Information and Computer Science.

QuICS Postdoctoral Fellows are expected to work in close collaboration with one or ideally more than one Center Fellows, and will have opportunities to interact with leading computer scientists and theoretical and experimental physicists at UMD and NIST. Successful applicants may focus on any area of quantum information processing. Applicants are encouraged to contact QuICS Fellows directly to inquire about current research interests.

The term of appointment is two years, with a competitive salary plus benefits and a small stipend for research expenses. The application deadline for full consideration is December 1, 2016, but applications may be considered until the positions are filled. Applicants should submit a Curriculum Vitae including a complete publication list and a two-page Research Statement, and should arrange for three reference letters. Applications are to be submitted through:
https://academicjobsonline.org/ajo/jobs/7899

Applicants who are U.S. citizens may also consider applying to the NRC Research Associateship Program. Possible advisors for these positions include Alexey Gorshkov, Stephen Jordan, Yi-Kai Liu, Jacob Taylor, and Eite Tiesinga. Before applying, you are encouraged to contact your potential adviser by email.

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Daniel Tiarks from the Max Planck Institute in Garching reports an optical phase shift of pi between two coherent state pulses with mean photon number below one, a big step towards deterministic optical quantum gates. The control pulse is first stored in a Rubidium ensemble using Rydberg EIT. The target pulse propagates through the ensemble, after a delay and with another EIT control beam, and collects a conditional phase. 

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Microsoft Supports Quantum Nanoscience Laboratory at Sydney University

A select and very small collection of labs worldwide are collaborating with Microsoft on quantum computing by doing revolutionary engineering and physics, including the Quantum Nanoscience Laboratory at the University of Sydney headed by Professor David Reilly – whose group is world-leading in understanding the interface between quantum physics and the grand engineering challenges of building reliable quantum machines.

#Quantum #QuantumResearch #QuantumComputing #QuantumComputer #QuantumPhysics #Australian #Australia #

http://www.quantumcomputingtechnologyaustralia.com/2016/04/22/microsoft-supports-quantum-nanoscience-laboratory-at-sydney-university/

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Quantum Computing Closer as RMIT Finds a Pathway Towards The Quantum Data Bus

RMIT researchers have trialled a quantum processor capable of routing quantum information from different locations, in a critical breakthrough for quantum computing. The work opens a pathway towards the “quantum data bus”, a vital component of future quantum technologies.

#Quantum #QuantumResearch #QuantumComputing #QuantumComputer #QuantumPhysics #Australian #Australia #RMIT #QuantumDataBus

http://www.quantumcomputingtechnologyaustralia.com/2016/04/19/quantum-computing-closer-as-rmitfinds-a-pathway-towards-the-quantum-data-bus/

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This articles a bit dated but it's one of the few more calm and reasoned discussions of superdeterminism I can find. This is a bit off topic as it's more philosophical rather than physics based but I'd like to opinion of anyone familiar with Quantum theory, especially computation. I can't recall where but I once heard that a good explanation for quantum entanglement in a superdeterministic universe was made clear by simple computational efficiency, but I'm not sure in exactly what manner that was meant.

Given the appearance of quantum non-locality being inferred by Bell's Theorem and the more common Copenhagen interpretation of QM, I'd like to invoke Occams's razor as likely pointing to superdeterminism over other QM interpretation because all other interpretations have to invoke Non-locality where as superdeterminism avoids this altogether by simply invoking an absolutly deterministic universe.

The philosophical implications of a lack of true free will are interesting but nothing that would cause an existential crisis or be grounds for invalidating the theory. As the article states, "But don't worry about it"

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Can the Quantum Eraser be seen as a quantum circuit?

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