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#### Physical Review A 50th Anniversary Milestones

The collection contains papers that have made important contributions to atomic, molecular, and optical physics and quantum information by announcing significant discoveries or by initiating new areas of research.

Collection

#### Two quantum Ising algorithms for the shortest-vector problem

Traditional public key cryptography will become obsolete when quantum computers are able to break it. The authors propose two quantum algorithms to solve the shortest-vector problem, which could play an important role in designing new cryptosystems for the postquantum era.

David Joseph, Adam Callison, Cong Ling, and Florian Mintert
Phys. Rev. A 103, 032433 (2021)

#### Direct double ionization of the ${\mathrm{Ar}}^{+}$ $M$ shell by a single photon

In this combined experimental and theoretical study, the authors report on the measurement of the absolute cross section for direct single-photon double ionization of Ar${}^{+}$, which is orders of magnitude smaller than the corresponding cross section for a neutral target. The experimental data are in very good agreement with the results of a theoretical approach which describes the dominant two-step-one process as the product of a single ionization and a subsequent half collision.

A. Müller et al.
Phys. Rev. A 103, L031101 (2021)

#### Quantum unary approach to option pricing

The authors present a quantum algorithm for the pricing of options, a financial derivative, which works in the unary representation of the value of the underlying asset. Compared to a previous binary algorithm, the present one is designed to be simple in terms of logic operations and in terms of connectivity requirements, while still giving sufficiently accurate results with less than 100 qubits.

Sergi Ramos-Calderer et al.
Phys. Rev. A 103, 032414 (2021)

#### Designing a physical quantum agent

A physical agent must interact with its environment using actuators (to act on the environment) and sensors (to read the environment). In this article, the authors show that an optical agent which interacts with its environment using quantum mechanical actuators and sensors can experience a dramatic enhancement in its ability to learn its environment, and they study the thermodynamic properties of learning in such a physical agent.

M. J. Kewming, S. Shrapnel, and G. J. Milburn
Phys. Rev. A 103, 032411 (2021)

#### Universal variational quantum computation

The author proves that the contemporary variational approach to quantum-enhanced algorithms enables a universal model of quantum computation. This brings the resources required for universal quantum computation closer to contemporary quantum processors.

Jacob Biamonte
Phys. Rev. A 103, L030401 (2021)

#### Nuclear polarization effects in atoms and ions

Nuclear structure effects lead to small corrections to electron energy-level shifts and isotope shifts in neutral atoms but have enhanced effects on heavy hydrogenlike ions. The authors analyze how nuclear structure effects scale with nuclear charge, mass number, and other parameters in various atoms and ions, with an emphasis on heavy hydrogenlike ions.

V. V. Flambaum, I. B. Samsonov, H. B. Tran Tan, and A. V. Viatkina
Phys. Rev. A 103, 032811 (2021)

#### Analytical expression for the electronic stopping cross section of atomic gas targets for hydrogen projectiles

The author derives an analytical expression for the electronic stopping cross section of atomic gas targets at nonrelativistic velocities for hydrogen ions. The expression is based on an ab initio approach to account for the electronic excitations and charge exchange processes at low collision energies and the correct Bethe approach at high collision energies.

R. Cabrera-Trujillo
Phys. Rev. A 103, 032812 (2021)

#### Eight Journals Introduce Letters

###### March 9, 2021

At the beginning of 2021, eight Physical Review journals began publishing Letters which are intended for the accelerated publication of important new results targeted to the specific readership of each journal.

#### Quantum degenerate mixtures of Cs and Yb

The authors experimentally demonstrate the production of quantum degenerate Bose-Bose mixtures of cesium and ytterbium with attractive and repulsive interactions through sympathetic cooling. This development adds another system to the ultracold-atom toolbox, enabling future studies of quantum droplets and binary fluid dynamics.

Kali E. Wilson, Alexander Guttridge, Jack Segal, and Simon L. Cornish
Phys. Rev. A 103, 033306 (2021)

#### High-energy-resolution measurements of an ultracold-atom–ion collisional cross section

The authors report on a method for scanning the collisional energies of a single ion with a cloud of ultracold atoms. This method is then applied to directly measure the collisional cross section between the two species, with high-energy resolution.

Ruti Ben-shlomi et al.
Phys. Rev. A 103, 032805 (2021)

#### Special Collection on Laser-Plasma Particle Acceleration

We are very pleased to offer the readers of Physical Review a new, carefully curated collection of articles from the vibrant field of laser-plasma particle acceleration. Some of the articles have already been published, and others will be forthcoming. This Collection is the latest in the journal’s series of Special Collections on current or emerging fields and topics.

#### Promoting Inclusive and Respectful Communications

###### November 18, 2020

APS Editor in Chief, Michael Thoennessen, discusses a new opportunity for communicating authors to include their pronouns together with their contact email in order to promote a more respectful, inclusive, and equitable environment.

###### FEATURED IN PHYSICS

Physicists working in optics, atomic and molecular physics, and quantum information reflect on landmark papers and how they influence research today.

Special Feature in

#### Current Issue

Vol. 103, Iss. 4 — April 2021

#### Announcements

##### APS Announces Outstanding Referees for 2021
###### February 24, 2021

APS has selected 151 Outstanding Referees for 2021 who have demonstrated exceptional work in the assessment of manuscripts published in the Physical Review journals. A full list of the Outstanding Referees is available online.

##### Special Collection on Laser-Plasma Particle Acceleration
###### November 30, 2020

We are very pleased to offer the readers of Physical Review X a new, carefully curated collection of articles from the vibrant field of laser-plasma particle acceleration. Some of the articles have already been published, and others will be forthcoming. This Collection is the latest in the journal’s series of Special Collections on current or emerging fields and topics.

##### Rapid Communications papers will now be Letters
###### November 23, 2020

Starting January 1, 2021, the Rapid Communications article type will be renamed to Letters. With this change, all eight Physical Review journals that had previously classified articles of the type “Rapid Communications” will adopt the practice of Physical Review Applied and now publish such articles as Letters. Learn more

##### Changes to the Sections of Physical Review A
###### July 1, 2020

We are reorganizing and modernizing the sectioning scheme of Physical Review A (PRA). As of July 1, 2020, the journal will include eight sections instead of the previous seven.

More Announcements

#### Job Openings

###### November 6, 2020

The editors of Physical Review A seek a dynamic and personable colleague for the position of Associate Editor. The primary responsibility is to manage the peer review process and decide, aided by expert input, which papers merit publication according to the journal’s criteria.