We propose a mechanism for testing the theory of collapse models such as continuous spontaneous localization (CSL) by examining the parametric heating rate of a trapped nanosphere. The random localizations of the center-of-mass for a given particle predicted by the CSL model can be understood as a stochastic force embodying a source of heating for the nanosphere. We show that by utilising a Paul trap to levitate the particle and optical cooling, it is possible to reduce environmental decoherence to such a level that CSL dominates the dynamics and contributes the main source of heating. We show that this approach allows measurements to be made on the timescale of seconds, and that the free parameter λ csl which characterises the model ought to be testable to values as low as 10 −12 Hz.

We show how charged levitated nano-and micro-particles can be cooled by interfacing them with an RLC circuit. All-electrical levitation and cooling is applicable to a wide range of particle sizes and materials, and will enable state-ofthe-art force sensing within an electrically networked system. Exploring the cooling limits in the presence of realistic noise we find that the quantum regime of particle motion can be reached in cryogenic environments both for passive resistive cooling and for an active feedback scheme, paving the way to levitated quantum electromechanics. arXiv:1802.05928v3 [quant-ph]

Associative memories are devices storing information that can be fully retrieved given partial disclosure of it. We examine a toy model of associative memory and the ultimate limitations it is subjected to within the framework of general probabilistic theories (GPTs), which represent the most general class of physical theories satisfying some basic operational axioms. We ask ourselves how large the dimension of a GPT should be so that it can accommodate 2 m states with the property that any N of them are perfectly distinguishable. Invoking an old result by Danzer and Grünbaum, we prove that when N = 2 the optimal answer to this question is m + 1, to be compared with O(2 m ) when the theory is required to be either classical or quantum. This yields an example of a task where GPTs outperform both classical and quantum theory exponentially. The same problem for N ≥ 3 is left open.

We present a technique for recovering the spectrum of a non-Markovian bosonic bath and/or non-Markovian noises coupled to an harmonic oscillator. The treatment is valid under the conditions that the environment is large and hot compared to the oscillator, and that its temporal autocorrelation functions are symmetric with respect to time translation and reflection -criteria which we consider fairly minimal. We model a demonstration of the technique as deployed in the experimental scenario of a nanosphere levitated in a Paul trap, and show that it can effectively probe the spectrum of an electric field noise source from 10 2 − 10 6 Hz with a high degree of accuracy (proportional to the reciprocal of the measurement time) owing to its unusually low noise floor. This technique may be deployed in quantum sensing, metrology, computing, and in experimental probes of foundational questions.

An investigation is described in which a high-sensitivity analytical balance of standard design is used for determination of the surface density of that thorium layer which corresponds to maximum thermionic emission with the thorium-on-tungsten system. Following Brattain and Becker's definition of this value of surface density as one ``f unit,'' thorium vapor is allowed to accumulate on a quartz plate until a weighable number of f units (about 600) has been deposited. The thorium flux in f units per minute is monitored periodically by means of a tungsten filament diode during the course of the deposition. Two polycrystalline specimens of ribbon from the same source have yielded the value of (4.2±0.2)1014 atoms/cm2 as the density for maximum emission. This is to be compared with a value of 5.0×1014 atoms/cm2 obtained in 1934 on theoretical grounds by Langmuir.