Events

Twisting the neutron wavefunction

Charles W. Clark, National Institute of Standards and Technology

Wave motions in water were already familiar in antiquity. The mathematical representation of waves in physics today is essentially the same as that first provided by d'Alembert and Euler in the mid-18th century. Yet it was only in the early 1990s that physicists managed to control a basic property of light waves: their capability of swirling around their own axis of propagation.

Public lecture by Charles W. Clark

Much of what we understand about the world comes from our eyes, which sense the colors from red to violet that are expressed in the rainbow.

Generation and Spectral Characterization of High-Purity Biphotons

Franco Wong, Massachusetts Institute of Technology

Spectrally factorable biphotons are highly desirable for many photonic quantum information processing tasks such as quantum computation, boson sampling, and quantum repeaters. We generate biphotons with spectral purity of 99%, the highest to date without any spectral filtering, by pulsed spontaneous parametric downconversion in a custom-fabricated PPKTP crystal under extended Gaussian phase-matching conditions.

Cybersecurity is Hard. Up for a Challenge?

Mark McArdle, eSentire

Pure technology approaches to cybersecurity consistently fail to prevent hackers from breaching networks and systems. The pursuit of a pure technology solution to cybersecurity is going to require significant breakthroughs in AI and machine learning. Come join a discussion about why cybersecurity is such a hard problem and review some promising areas of research that may bring positive changes.

Efficient Quantum Algorithms for Simulating Lindblad Evolution

Chunhao Wang

The Lindblad equation is the natural generalization to open systems of the Schrödinger equation. We give a quantum algorithm for simulating the evolution of an n-qubit system under the Lindblad equation with local terms. The gate cost of the algorithm is O(mTlog^2(T/\epsilon)/loglog(T/\epsilon)), where T is the evolution time, \epsilon is the precision of the output state, and m is the number of local terms occurring in the equation.

Graphs and Multi-mode Coupling: How to build a programmable, directional parametric amplifier

Jose Aumentado, National Institute of Standards and Technology, Boulder

Parametric amplification is a big deal these days, especially for research in superconducting quantum information. This is because, in principle, parametric amplifiers can amplify a signal while adding the minimum amount of noise that quantum mechanics allows. In practice, the situation is a little more complicated and the practical measurement chains can degrade this ideal performance.

Entanglement and Purcell Effects in Systems for Quantum Information and Sensing

Stephen K. Gray, Argonne National Laboratory

I discuss how to propagate the quantum mechanical density matrix, including dephasing, spontaneous emission and dissipation for systems relevant to quantum information and sensing. Two applications are then presented. In the first example, a plasmonic system is coupled to quantum dots. The plasmonic system could be a single metal nanoparticle or an array of metal nanoparticles and can be viewed as an optical resonator.

Dicke's Superradiance in Astrophysics

Fereshteh Rajabi, University of Western Ontario

It is generally assumed that in the interstellar medium much of the emission emanating from atomic and molecular transitions within a radiating gas happen independently for each atom or molecule, but as was pointed out by R. H. Dicke in a seminal paper several decades ago this assumption does not apply in all conditions. As will be discussed in my presentation, and following Dicke's original analysis, closely packed atoms/molecules can interact with their common electromagnetic field and radiate coherently through an effect he named superradiance.

Structured Hadamard matrices and quantum information

Karol Zyczkowski, Jagiellonian University, Poland

Two classes of complex Hadamard matrices with certain special properties found recently applications in quantum physics. Consider a four index tensor $T_{ijkl}$ of size M. It can be reshaped into a square matrix $A_{\mu,\nu}$ of size $M^2$ with three different choices of composed indices e.g. $\mu=(i,j); \nu=(k,l)$ or $\mu=(i,k); \nu=(j,l)$, or $\mu=(i,l); \nu=(j,k)$.

Exponential Separation between Quantum Communication Complexity and Classical Information Complexity

Dave Touchette, IQC

We exhibit a Boolean function for which the quantum communication complexity is exponentially larger than the classical information complexity. An exponential separation in the other direction was already known from the work of Kerenidis et. al. [SICOMP 44, pp. 1550--1572], hence our work implies that these two complexity measures are incomparable. As classical information complexity is an upper bound on quantum information complexity, which in turn is equal to amortized quantum communication complexity, our work implies that a tight direct sum result for distributional quantum communication complexity cannot hold.