Reciprocity is a fundamental physical principle that roots in the time‐reversal symmetry of physical laws. It allows making predictions on any arbitrary complex system's response and operation and hence simplifies the analysis. However, there are many practical situations in which it is advantageous to break reciprocity, e.g., isolators preventing wave scattering back to lasers and generators, full‐duplex systems for multiplexing transmission and receiving in the same channel, nonreciprocal cavity excitation, and protection of fragile states of superconductor quantum computers from thermal noise. The most widespread approach to time‐reversal symmetry breaking and nonreciprocity based on magnetic field biasing suffers from bulkiness, cost ineffectiveness, and loss, motivating researchers and engineers to search for more practical approaches. Herein, the up‐and‐coming advances in optical nonreciprocity, including new materials (Weyl semimetals, topological insulators, metasurfaces), active structures, time‐modulation, parity‐time (PT)‐symmetry breaking, nonlinearity combined with a structural asymmetry, quantum nonlinearity, unidirectional gain and loss, chiral quantum states and valley polarization are overviewed. A general description of nonreciprocal systems is provided and the pros and cons of the mentioned approaches to nonreciprocity are discussed.

Quantum computers (QC), if realized, could disrupt many computationally intense fields of science. The building block element of a QC is a quantum bit (qubit). Qubits enable the use of quantum superposition and multi-state entanglement in QC calculations, allowing a QC to simultaneously perform millions of computations at once. However, quantum states stored in a qubit degrade with decreased quality factors and interactions with the environment. One technical solution to improve qubit lifetimes and network interactions is a circuit comprised of a Josephson junction-based qubit located inside of a high Q-factor superconducting 3D cavity. It is known that niobium resonators can reach Q 0 > 10 11. However, existing cavity geometries are optimized for particle acceleration rather than hosting qubits. RadiaBeam Technologies, in collaboration with Argonne National Laboratory and The University of Chicago, has developed a niobium superconducting radio frequency quarter-wave resonant cavity (QWR) for quantum computation. A 6 GHz QWR was optimized to include tapering of the inner and outer conductors, a toroidal shape for the resonator shorting plane, and an inner conductor tip to reduce parasitic capacitance. In this paper, we present the results of the resonator design optimization, fabrication, processing, and testing. 1 Introduction Nearly all areas of modern life are influenced by the incredible impact of computational capabilities. Quantum computers may make many computationally intense fields of science, such as cosmology, quantum field theory, particle interactions, and nuclear physics, tractable. The building block element of a QC is a quantum bit, which is a two-level quantum system. Qubits enable the use of quantum superposition and multi-state entanglement in QC calculations, allowing a QC to perform millions of quantum mechanical computations at once [1]. Entanglement lets a QC change the state of multiple qubits simultaneously via adjusting the state stored in a single bit, enabling computational power scalability unachievable with traditional computers [2]. These advantages are not just theoret

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The Facility for Rare Isotope Beams (FRIB) will be a new scientific user facility that produces rare-isotope beams for experiments from the fragmentation of heavy ions at energies of 100–200 MeV/u. During the projectile fragmentation, the rare isotope of interest is produced along with many contaminants that need to be removed before the beam reaches detectors. At FRIB, this is accomplished with a magnetic projectile fragment separator. However, to achieve higher beam purity, in particular for proton-rich rare isotopes, additional purification is necessary. RadiaBeam in collaboration with Michigan State University (MSU) has designed a 20.125 MHz radiofrequency (RF) fragment separator capable of producing a 4 MV kick with 18 cm aperture in order to remove contaminant isotopes based on their time of flight. In this paper, we will discuss the RF and engineering design considerations of this separator cavity.