Density matrix

Formal sciences
Theoretical computer science
Theory of computation
Quantum computing

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Variational Quantum Monte Carlo Method with a Neural-Network Ansatz for Open Quantum Systems

Vincenzo Savona, Alexandra Nagy

The possibility to simulate the properties of many-body open quantum systems with a large number of degrees of freedom (d.o.f.) is the premise to the solution of several outstanding problems in quantum science and quantum information. The challenge posed b ...

AMER PHYSICAL SOC2019

Imaging electron-density fluctuations by multidimensional X-ray photon-coincidence diffraction

Jérémy Raymond Jean Maurice Rouxel

The ultrafast spontaneous electron-density fluctuation dynamics in molecules is studied theoretically by off-resonant multiple X-ray diffraction events. The time- and wavevector-resolved photon-coincidence signals give an image of electron-density fluctuat ...

National Academy of Sciences2019

SPINE (SPIN Emulator) - A Quantum-Electronics Interface Simulator

Edoardo Charbon, Fabio Sebastiano

A quantum computer comprises a quantum processor and the associated control electronics used to manipulate the qubits at the core of a quantum processor. CMOS circuits placed close to the quantum bits and operating at cryogenic temperatures offer the best ...

IEEE2019

Fourier dimensionality reduction for fast radio transients

Jean-Philippe Thiran, Yves Wiaux, Vijay Kartik, Ming Jiang

In the context of next-generation radio interferometers, we are facing a big challenge of how to economically process data. The classical dimensionality reduction technique, averaging visibilities on time, may dilute fast radio transients (FRT). We propose ...

2019

Near-Optimal Finite-Length Scaling for Polar Codes Over Large Alphabets

Rüdiger Urbanke, Henry Pfister

For any prime power q, Mori and Tanaka introduced a family of q-ary polar codes based on the q x q Reed-Solomon polarization kernels. For transmission over a q-ary erasure channel, they also derived a closed-form recursion for the erasure probability of ea ...

2019

Atom-density representations for machine learning

Michele Ceriotti, Félix Benedito Clément Musil, Michael John Willatt

This has led to a proliferation of alternative ways to convert an atomic structure into an input for a machine-learning model. We introduce an abstract definition of chemical environments that is based on a smoothed atomic density, using a bra-ket notation ...

2019

Convergence of the Exponentiated Gradient Method with Armijo Line Search

Volkan Cevher, Yen-Huan Li

Consider the problem of minimizing a convex differentiable function on the probability simplex, spectrahedron, or set of quantum density matrices. We prove that the expo-nentiated gradient method with Armijo line search always converges to the optimum, if ...

2019

Driven-dissipative quantum Monte Carlo method for open quantum systems

Vincenzo Savona, Alexandra Nagy

We develop a real-time full configuration-interaction quantum Monte Carlo approach to model driven-dissipative open quantum systems with Markovian system-bath coupling. The method enables stochastic sampling of the Liouville–von Neumann time evolution of t ...

2018

Structure from sound with incomplete data

Martin Vetterli, Ivan Dokmanic, Gilles Baechler, Miranda Krekovic

In this paper, we consider the problem of jointly localizing a microphone array and identifying the direction of arrival of acoustic events. Under the assumption that the sources are in the far field, this problem can be formulated as a constrained low-ran ...

2018

Tuning adatom mobility and nanoscale segregation by twin formation and polytypism

Anna Fontcuberta i Morral, Federico Matteini, Luca Francaviglia, Gözde Tütüncüoglu

Nanoscale variations in the composition of an AlxGa1−xAs shell around a GaAs nanowire affect the nanowire functionality and can lead to the formation of localized quantum emitters. These composition fluctuations can be the consequence of variations of crys ...

2018

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