Yu Tian, and Renaud Lambiotte. “Spreading and Structural Balance on Signed Networks.” arXiv preprint arXiv:2212.10158 (2022).
Link: https://arxiv.org/abs/2212.10158
Popular summary: Two competing types of interactions often play an important part in shaping system behavior, such as activatory or inhibitory functions in biological systems. Hence, signed networks, where each connection can be either positive or negative, have become popular models over recent years. In this paper, we first introduce a classification of signed networks into balanced, antibalanced or strictly balanced ones, and then characterize each type of signed networks in terms of the spectral properties of the signed weighted adjacency matrix. These properties are important to understand the dynamics on signed networks, both linear and nonlinear ones. Specifically, we find consistent patterns in a linear and a nonlinear dynamics theoretically, depending on their type of balance. Finally, we numerically verify these properties through experiments on both synthetic and real networks.
Sreenath K. Manikandan, and Sofia Qvarfort. “Optimal quantum parametric feedback cooling.” arXiv preprint arXiv:2204.00476 (2022).
Link: https://arxiv.org/abs/2204.00476
Popular summary: In quantum systems that consist of many atoms, such as small levitated beads, it becomes crucial to reduce noise in the system. One source of noise is thermal motion of the atoms, which is why many quantum systems must be cooled to their ground state (which is the lowest energy level they can be at). A common method in levitated quantum systems is to change the width of the confinement potential in time, which slows the oscillations of the system. This is known as parametric feedback cooling, and is similar to a child on a swing, who will use their legs to slow down the back-and-forth motion. In this paper, we derive the best-possible limit to cooling using parametric feedback cooling the quantum regime. The results can help to better develop cooling protocols for levitated systems in the quantum regime.
Sofia Qvarfort, and Igor Pikovski. “Solving quantum dynamics with a Lie algebra decoupling method.” arXiv preprint arXiv:2210.11894 (2022).
Link: https://arxiv.org/abs/2210.11894
Popular summary: As we become better and better at controlling quantum systems in the laboratory, it becomes crucial to understand and accurately model the dynamics. In this paper, which is aimed at physics PhD students, we provide a pedagogical introduction to a method that uses a mathematical structure known as a Lie algebra for solving quantum dynamics. The results can help us develop better models of quantum systems, which ultimately provides tools for developing quantum technologies.
Yuxun Ling, Sofia Qvarfort, and Florian Mintert. “Fast Optomechanical Photon Blockade.” arXiv preprint arXiv:2212.00628 (2022).
Link: https://arxiv.org/abs/2212.00628
Popular summary: In many quantum technologies, it is crucial to have access to devices that produce a single photon with high accuracy. In optomechanical systems, an optical mode in (e.g. laser light) in a cavity is used to manipulate and control a small mechanical element (such as a microscopic mirror). Under specific circumstances, the interaction between the laser and the mechanical element gives rise to a situation where only a single photon can exist in the cavity for a specific duration, known as photon blockade. In this paper, we show that using laser light at two different frequencies allows us to tune the system so that photon blockade occurs quickly after the initialisation of the system. The results show that this additional control can help improve on existing schemes that have been developed for optomechanical systems.
Lydia A. Kanari-Naish, et al. “Two-mode Schrödinger-cat states with nonlinear optomechanics: generation and verification of non-Gaussian mechanical entanglement.” Quantum Science and Technology 7.3 (2022): 035012.
DOI: https://doi.org/10.1088/2058-9565/ac6dfd
Popular summary: One of the most well-known examples of quantum mechanics is Schrödingers cat, where a cat is placed in a superposition of being both dead and alive at the same time. When two cat-states exhibit correlations that cannot be described in classical physics, we say that they are entangled. In optomechanical systems, we use light or another radiation mode to control a small mechanical element, such as a microscopic mirror. When such an element is placed in a distinctive superposition state, we call it a cat-state. In this paper, we develop a scheme for pulsing light through two cavities, such that it interacts with a mechanical element placed in each cavity. By then measuring the light in a specific way, we can herald the preparation of two entangled cat-states. We also show that by using a secondary light-pulse, it is possible to perform measurements that verify the entanglement. The work has implications for the preparation of mechanical cat-states using pulsed optomechanics.
Sofia Qvarfort, Dennis Rätzel, and Stephen Stopyra. “Constraining modified gravity with quantum optomechanics.” New Journal of Physics 24.3 (2022): 033009.
Link: https://doi.org/10.1088/1367-2630/ac3e1b
Popular summary: There is a large discrepancy between the predictions of General Relativity and Particle Physics regarding the value of vacuum energy, which is often called the most embarrassing problem in modern physics. By introducing modifications to General Relativity, this problem can be addressed. However, since the predictions of General Relativity have already been confirmed through a variety of tests, these modifications must either be extremely small or very difficult to detect. In this paper, we consider the extent to which an optomechanical system (where an optical mode is used to measure and control a mechanical mode) can be used to constrain a common family of modified gravity theories. We find that, in the ideal case, some constraints can be improved, but that the large mass of the optomechanical system introduces additional challenges for detecting the modifications. The work has implications for testing fundamental physics and improving our understanding of gravity.
Manikandan, S. K., Elouard, C., Murch, K. W., Auffèves, A., & Jordan, A. N. (2022). Efficiently fueling a quantum engine with incompatible measurements. Physical Review E, 105(4), 044137. (https://journals.aps.org/pre/abstract/10.1103/PhysRevE.105.044137)
Popular summary: We propose quantum engines fueled by measurements of incompatible observables of a quantum oscillator. The engine presents a one quantum advantage for work extraction by converting the quantum measurement added noise to produce useful work. The engine produces non-zero work even at zero temperature (beating known classical limits for extractable work) which can be tested in experiments.
Yanik, Kagan, Bibek Bhandari, Sreenath K. Manikandan, and Andrew N. Jordan. “Thermodynamics of quantum measurement and Maxwell’s demon’s arrow of time.” Physical Review A 106, no. 4 (2022): 042221. (https://journals.aps.org/pra/abstract/10.1103/PhysRevA.106.042221)
Popular summary: We envision a qubit engine fueled by quantum measurements and feedback control by a Maxwell’s demon. We relate the exact finite time statistics of heat, extractable work, and entropy changes, to an information theoretic measure of the demon’s perceived arrow of time, which can be tested in experiments. This work was editor’s suggestion in Phys. Rev. A.
Manikandan, Sreenath K., and Karthik Rajeev. “New kind of echo from quantum black holes.” Physical Review D 105, no. 6 (2022): 064024. (https://journals.aps.org/prd/abstract/10.1103/PhysRevD.105.064024)
Popular summary: We make testable predictions for superfluid quantum condensate descriptions for black hole horizons. By making comparisons to an analogous scenario in condensed matter, we predict that such considerations should modify the reflectivity and dispersion relations near the event horizon and produce echoes of the gravitational wave signals, which should be measurable in the ring-down phase of a merger event.
Manikandan, Sreenath K. “Autonomous quantum clocks using athermal resources.” arXiv preprint arXiv:2207.07909 (2022). (https://arxiv.org/abs/2207.07909)
Popular summary: We propose quantum clocks which produce ticks autonomously, fueled by simultaneous measurements of quantum spin and fluorescence. These quantum clocks are comparable to clocks driven by a chemical potential gradient (as opposed to thermal clocks), and tick at more regular intervals than a Poissonian clock.
Karmakar, Tathagata, Étienne Jussiau, Sreenath K. Manikandan, and Andrew N. Jordan. “Cyclic superconducting quantum refrigerators using guided fluxon propagation.” arXiv preprint arXiv:2212.00277 (2022). (https://arxiv.org/abs/2212.00277)Popular summary: We propose quantum refrigerators using vortices in a type II superconductor as the working substance. These refrigerators have a working mechanism comparable to domestic refrigerators; fluxons carry heat in loops from the cold to the hot reservoir, facilitated by adiabatic variations in an applied magnetic field gradient across the loop. The refrigerator can be integrated to quantum circuits, where we estimate a cooling power of 10nW under normal operating conditions.
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