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The Majorana stellar representation is used to characterize spin states that have a maximally negative Wigner quasiprobability distribution on a spherical phase space. These maximally Wigner-negative spin states generally exhibit a partial but not high degree of symmetry within their star configurations. In particular, for spin $j > 2$, maximal constellations do not correspond to a Platonic solid when available and do not follow an obvious geometric pattern as dimension increases. In addition, they are generally different from spin states that maximize other measures of nonclassicality such as anticoherence or geometric entanglement. Random states ($j \leq 6$) display on average a relatively high amount of negativity, but the extremal states and those with similar negativity are statistically rare in Hilbert space. We also prove that all spin coherent states of arbitrary dimension have non-zero Wigner negativity. This offers evidence that all pure spin states also have non-zero Wigner negativity. The results can be applied to qubit ensembles exhibiting permutation invariance.

We show that currently available noisy intermediate-scale quantum (NISQ) computers can be used for versatile quantum simulations of chaotic systems. We introduce a novel classical-quantum hybrid approachfor exploring the dynamics of the chaotic quantum kicked top (QKT) on a universal quantum computer. The programmability of this approach allows us to experimentally explore the complete range of QKT chaoticity parameter regimes inaccessible to previous studies. Furthermore, the number of gates in our simulation does not increase with the number of kicks, thus making it possible to study the QKT evolution for arbitrary number of kicks without fidelity loss. Using a publicly accessible NISQ computer (IBMQ), we observe periodicities in the evolution of the 2-qubit QKT, as well as signatures of chaos in the time-averaged 2-qubit entanglement. We also demonstrate a connection between entanglement and delocalization in the 2-qubit QKT, confirming theoretical predictions.

We show that introducing a small uncertainty in the parameters of quantum systems can make the dynamics of these systems robust against perturbations. Concretely, for the case where a system is subject to perturbations due to an environment, we derive a lower bound on the fidelity decay, which increases with increasing uncertainty in the state of the environment. Remarkably, this robustness in fidelity can be achieved even in fragile chaotic systems. We show that non-Markovianity is necessary for attaining robustness in the fidelity., 5 pages, 2 figures

The visibility of women and the awareness of a healthy gender balance in physics in the Netherlands have clearly improved over the last few years. Initiatives to promote women and their possibilities to pursue a career in physics are plentiful and commendable. Nevertheless, the numbers do not yet show the desired impact of all these initiatives. Although student numbers have increased, the percentage of female first-year student remains at approximately 13% of the total students in physics. Similarly, the relative numbers of female PhD candidates and postdocs have been stable over the last years at (both) approximately 20% to 25%. Despite the number of women obtaining a PhD in physics and continuing a scientific career as postdoc, the presence of women further up on the scientific ladder in physics remains strikingly low. We will here focus on the current status, ambitions, and initiatives in the Netherlands to promote women, and especially to keep them, in physics.

We present two hyperentanglement concentration schemes for two-photon states that are partially entangled in the polarization and time-bin degrees of freedom. The first scheme distills a maximally hyperentangled state from two identical less-entangled states with unknown parameters via the Schmidt projection method. The other scheme can be used to concentrate an initial state with known parameters, and requires only one copy of the initial state for the concentration process. Both these two protocols can be generalized to concentrate N-photon hyperentangled Greenberger- Horne-Zeilinger states that are simultaneously entangled in the polarization and time-bin degrees of freedom. Our schemes require only linear optics and are feasible with current technology. Using the time-bin degree of freedom rather than the spatial mode degree of freedom can provide savings in quantum resources, which makes our schemes practical and useful for long-distance quantum communication., Comment: 7 pages

We present a scheme for optimal joint remote state preparation of two-qubit equatorial states. Our protocol improves on a previous scheme (B. S. Choudhury and A. Dhara 2015 Quantum Inf. Process. 14 373) that had a success probability of 25%, which increased to 50% when extra classical information is sent to the receiver. We show that using our modified scheme, the desired state can be prepared deterministically with the same quantum channel. Moreover, we generalize the scheme to prepare N-qubit equatorial states in which the receiver can reconstruct the original state with 100% success probability., Comment: 6 pages

We propose a 2N qubit entangled channel that can be used to teleport N qubits in a network to a single receiver. We describe the construction of this channel and explicitly demonstrate how the protocol works. The protocol is different from teleportation using $N$ Bell pairs shared between $N$ senders and a single receiver, as it ensures that all parties have to participate in order for the teleportation to be successful. This can be advantageous in various scenarios and we discuss potential application of this protocol to voting.

In this paper, a detailed analysis of anisotropic effects on the phonon induced spin relaxation rate in III-V semiconductor quantum dots (QDs) is carried out. We show that the accidental degeneracy due to level crossing between the first and second excited states of opposite electron spin states in both isotropic and anisotropic QDs can be manipulated with the application of externally applied gate potentials. In particular, anisotropic gate potentials enhance the phonon mediated spin-flip rate and reduce the cusp-like structure to lower magnetic fields, in addition to the lower QDs radii in III-V semiconductor QDs. In InAs QDs, only the Rashba spin-orbit coupling contributes to the phonon induced spin relaxation rate. However, for GaAs QDs, the Rashba spin-orbit coupling has a contribution near the accidental degeneracy point and the Dresselhaus spin-orbit coupling has a contribution below and above the accidental degeneracy point in the manipulation of phonon induced spin relaxation rates in QDs., Comment: 7 pages, 5 figures

Effective science education requires the ongoing development of teaching tools that take advantage of current technology and can adjust to the changing patterns of student learning. The Laurier Undergraduate Physics Online Database (UPOD) is an online handbook of physics content being developed by Laurier students. This is the first physics handbook written by students for students (all material is also checked by a faculty member). The first version of the website is online at http://upod.ca/. The goal is to create a novel online resource for faculty and students at Laurier and elsewhere. In today’s fast-paced world, students face demands on their time from multiple activities. By utilizing the power of the Internet, we can streamline students’ learning of physics. The hierarchical and lateral organization and links between topics in the website creates a ‘roadmap’ connecting key ideas, thus providing a concise, consistent and unifying picture of physics. The UPOD will be a learning tool for over 800 students enrolled in 1st year physics/astronomy courses at WLU every year. An important goal is to help beginning students improve their performance and thus reduce attrition in science programs. The advanced level topics can help physics as well as other science majors. This project also provides an excellent learning experience for students who develop the website. The website has received positive feedback from students and is beginning to be accessed by users from around the world. The next step will be to assess its effectiveness as a learning tool.

Continuous observation of a quantum system yields a measurement record that faithfully reproduces the classically predicted trajectory provided that the measurement is sufficiently strong to localize the state in phase space but weak enough that quantum backaction noise is negligible. We investigate the conditions under which classical dynamics emerges, via continuous position measurement, for a particle moving in a harmonic well with its position coupled to internal spin. As a consequence of this coupling we find that classical dynamics emerges only when the position and spin actions are both large compared to $\hbar$. These conditions are quantified by placing bounds on the size of the covariance matrix which describes the delocalized quantum coherence over extended regions of phase space. From this result it follows that a mixed quantum-classical regime (where one subsystem can be treated classically and the other not) does not exist for a continuously observed spin 1/2 particle. When the conditions for classicallity are satisfied (in the large-spin limit), the quantum trajectories reproduce both the classical periodic orbits as well as the classically chaotic phase space regions. As a quantitative test of this convergence we compute the largest Lyapunov exponent directly from the measured quantum trajectories and show that it agrees with the classical value., Comment: 8 pages, 5 figures