Seminar

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Monday, March 2, 2015 11:00 am - 12:00 pm EST (GMT -05:00)

Thomas Babinec: Quantum Photonic Devices Based on Single Dopants in Solids

Thomas Babinec, Stanford University

Tremendous progress has been made in the development of high-purity semiconductor materials so that their optoelectronic properties can now be controlled at the level of a single active dopant1. These individual impurities, which are quantum systems embedded in a solid-state host, possess diverse applications in quantum information science and technology2. As a simple and noteworthy example, single photons emitted from an optically active dopant may be used to share secure bits via quantum cryptographic key distribution3.

Monday, March 9, 2015 2:30 pm - 3:30 pm EDT (GMT -04:00)

Andrew Briggs: The Oxford Questions – and some answers

Andrew Briggs, Oxford

At a conference in Oxford in 2010 a set of questions was formulated with a view to establishing an agenda for subsequent research in quantum reality. Some of these questions are open to experimental investigation. We have since performed tests of the Leggett-Garg inequality in two and in three level systems, in each case violating the condition for macrorealism. We are now addressing another of the questions in single molecule devices using nanofabricated gaps in graphene.

Wednesday, March 18, 2015 1:30 pm - 2:30 pm EDT (GMT -04:00)

Ty Volkoff: Schrodinger cat states in separable Hilbert space: optimal branch distinguishability and algebras for metrological usefulness

Ty Volkoff, University of California, Berkeley

Two measures of macroscopicity for quantum superpositions in countably infinite dimensional Hilbert space will be introduced: one depending on the optimal distinguishability of the components of the superposition under measurements of subsets of particles and another based on the ratio of the quantum Fisher information of the superposition to that of its components.

Friday, February 13, 2015 1:30 pm - 2:30 pm EST (GMT -05:00)

David McKay: High contrast interactions and photonic qubits using multimode cavity QED

David McKay, University of Chicago

Superconducting Josephson‐junction (JJ) qubits are an emerging technology for quantum information processing. These qubits can be engineered with strong coupling to two or three‐dimensional microwave cavities which implements the cavity quantum electrodynamics (QED)  paradigm ‐ coherent coupling of a two‐level system to a harmonic oscillator. Cavity QED enables high fidelity qubit state readout, cavity‐mediated two‐qubit gates, and storing quantum information in noise‐insensitive photonic states.

Tuesday, February 24, 2015 10:30 am - 11:30 am EST (GMT -05:00)

Adam Tsen: Weakly Bound and Strongly Interacting: 1T-TaS2 in the Two-Dimensional Limit

Adam Tsen,  Columbia University

Among the most intriguing aspects of reduced dimensionality in solids is the enhancement of correlation effects (electron-electron, electron-phonon, etc.). In the layered metallic chalcogenides, this gives rise to the formation of various collective electron phases such as charge density waves (CDWs), spin density waves, and superconductivity.

Thursday, February 19, 2015 12:00 pm - 1:00 pm EST (GMT -05:00)

Viv Kendon: Ancilla mediated quantum gates

Viv Kendon, Durham University

Practical quantum gate operations for quantum computing usually take
advantage of extra degrees of freedom in a physical qubit system or use
an extra, ancilla, system. For example, the collective vibrational
modes of ions in a trap are used for the Cirac-Zoller gate. I will
describe our search for the simplest forms of ancilla-controlled quantum
operations. Solving this theoretical puzzle can potentially lead us to
simpler designs for quantum computers that are easier to build. This

Tuesday, February 10, 2015 10:30 am - 11:30 am EST (GMT -05:00)

Nathalie de Leon: Diamond nanophotonics for solid state quantum optics

Nathalie de Leon - Harvard University

Large-scale quantum networks will require efficient interfaces between photons and stationary quantum bits. Nitrogen vacancy (NV) centers in diamond are a promising candidate for quantum information processing because they are optically addressable, have spin degrees of freedom with long coherence times, and as solid-state entities, can be integrated into nanophotonic devices.

Thursday, February 12, 2015 12:00 pm - 1:00 pm EST (GMT -05:00)

Niel de Beaudrap: On computation with 'probabilities' modulo k

Niel de Beaudrap, IQC

Probability distributions and quantum states are examples of abstract
"distributions" over information such as bit-strings, in which more
than one bit-string may be a possible outcome. Probability
distributions are vectors of non-negative reals; quantum states are
vectors of complex-valued amplitudes, which may interfere
destructively. To investigate the importance of destructive
interference of "possibilities" independently of quantum mechanics, we

Monday, February 9, 2015 2:30 pm - 3:30 pm EST (GMT -05:00)

Jens Koch: Open-system quantum simulation with photons

Jens Koch, Northwestern University

Quantum simulators such as systems of ultracold atoms in optical lattices enable one to explore exotic quantum phases of matter and systematically study quantum phase transitions between them. Recently demonstrated photonic systems based on circuit QED (Quantum ElectroDynamics) arrays feature exciting properties that set them apart from these conventional quantum simulators. In particular, a crucial difference is the intrinsic open-system character of photon-based systems.

Monday, February 9, 2015 1:00 pm - 2:00 pm EST (GMT -05:00)

Swati Singh: Coupling single quantum systems to spin baths

Swati Singh, Harvard

The study of the interaction between quantum systems and their environment is central to the understanding of a broad range of problems. Important examples include the elusive quantum to classical transition, as illustrated most famously by the Schrödinger cat paradox, and non-equilibrium dynamics, as illustrated by the central spin problem. On the applied side, this understanding is an essential step towards quantum metrology, including the development of quantum noise limited detectors.