A number of quantum technologies require macroscopic mechanical oscillators possessing ultra-high motional Q-factors. These can be used to explore the macroscopic limits of quantum mechanics, to develop quantum sensors and to test the quantum nature of gravity. One approach is to trap nanometer to micron-sized particles in 3D; however, the use of ion or optical traps suffers from a number of difficulties including electrodynamic noise due to patch fields, damage to the particles due to unwanted laser heating, or difficulty in reaching low pressures due to particle loss. In this work, we report a completely passive, magnetic trap which confines a micro-diamond in 3D and which requires no active power—optical or electrical. We design, model, fabricate, and test the operation of our magneto-mechanical trap and experimentally demonstrate trapping down to ∼0.1 Torr. We measure the position fluctuation of the trapped micro-diamond as a function of pressure and find good agreement with Brownian theory.

The nature of quasiparticles in 2D quantum antiferromagnets at finite temperature remains an open question despite decades of theoretical work. In particular, it is not fully understood how long wavelength excitations contribute to significant broadening of the experimentally observable spectrum. Motivated by this problem, we consider the XY model of easy-plane antiferromagnets, and compute the dynamic structure factor by direct summation of diagrams. In doing so, we find that non-interacting quasiparticles with infinite lifetimes can still lead to a broad response. This forms the basis for a new paradigm describing the interaction of experimental probes with a physical system, where broadening is due neither to the lifetime, nor to the emergence of fractional quasiparticles. Instead, strong fluctuations drive the probe to absorb and radiate an infinite number of arbitrarily low energy quasiparticles, leading us to draw parallels with the infrared catastrophe in quantum electrodynamics.

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Development of acoustic and optoacoustic on-chip technologies calls for new solutions to guiding, storing and interfacing acoustic and optical waves in integrated silicon-on-insulator systems. One of the biggest challenges in this field is to suppress the radiative dissipation of the propagating acoustic waves, while co-localizing the optical and acoustic fields in the same region of an integrated waveguide. Here we address this problem by introducing anti-resonant reflecting acoustic waveguides (ARRAWs)—mechanical analogues of the anti-resonant reflecting optical waveguides. We discuss the principles of anti-resonant guidance and establish guidelines for designing efficient ARRAWs. Finally, we demonstrate examples of the simplest silicon/silica ARRAW platforms that can simultaneously serve as near-IR optical waveguides, and support strong backward Brillouin scattering.

Two-dimensional Heisenberg antiferromagnets play a central role in quantum magnetism, yet the nature of dynamic correlations in these systems at finite temperature has remained poorly understood for decades. We solve this long-standing problem by using a quantum-classical duality to calculate the dynamic structure factor analytically and, paradoxically, find a broad frequency spectrum despite the very long quasiparticle lifetime. The solution reveals multiscale physics whereby an external probe creates a classical radiation field containing infinitely many quanta. Crucially, it is the multiscale nature of this phenomenon which prevents a conventional renormalization group approach. We also challenge the common wisdom on static correlations and perform Monte Carlo simulations which demonstrate excellent agreement with our theory.