Efficient Quantum Algorithms for GHZ and W States, and Implementation on the IBM Quantum Computer (Adv. Quantum Technol. 5‐6/2019)

Abstract

Entanglement is a fundamental resource in quantum information and technology. In article number 1900015, Clément Javerzac‐Galy and co‐workers investigate efficient new algorithms to create N‐qubit Greenberger–Horne–Zeilinger (GHZ) and W states with time‐complexity scaling linearly and logarithmically in N. Quantum circuits are implemented on the IBM quantum computer up to N = 16, and entanglement is investigated through tomography (and other methods) as shown in the cover picture. While the fidelity decreases with increasing N, it does so more slowly for the logarithmic algorithms. (Image design by Chun Lam Chan.)

Revisiting the generalized pseudospectral method: Energy degeneracies, radial expectation values, and Schwarz‐like inequalities of the shell‐confined atom

“…We finally showed that in the extreme situation of the inner radius coalescing with the outer radius, the electron becomes a classical particle. With the increasing interest in spherically confined multi‐electron atoms in recent years, it is worth mentioning that the GPS method developed here could potentially serve as a powerful numerical tool for solving the one‐electron equation in other sophisticated approximations for confined multi‐electron systems, for example, the self‐consistent Hartree–Fock method [49–51] and the density‐functional theory [52–55].…”

Ground-state calculations of confined hydrogen molecule H2 using variational Monte Carlo method

“…It guarantees that ( = , ) = 0 at the boundary. This factor has been successfully used in previous variational studies of atoms confined by padded spherical walls [28] and becomes the usual cut-off term for an infinitely hard wall when = 1, as discussed in [12]. This type of cut-off function was found to provide accurate results.…”