Recent Noteworthy Physics Papers

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I. Marinković et al., "Optomechanical Bell Test", Phys. Rev. Lett., 121, 220404 (2018).

Abstract: Over the past few decades, experimental tests of Bell-type inequalities have been at the forefront of understanding quantum mechanics and its implications. These strong bounds on specific measurements on a physical system originate from some of the most fundamental concepts of classical physics—in particular that properties of an object are well-defined independent of measurements (realism) and only affected by local interactions (locality). The violation of these bounds unambiguously shows that the measured system does not behave classically, void of any assumption on the validity of quantum theory. It has also found applications in quantum technologies for certifying the suitability of devices for generating quantum randomness, distributing secret keys and for quantum computing. Here we report on the violation of a Bell inequality involving a massive, macroscopic mechanical system. We create light-matter entanglement between the vibrational motion of two silicon optomechanical oscillators, each comprising approx. 1010 atoms, and two optical modes. This state allows us to violate a Bell inequality by more than 4 standard deviations, directly confirming the nonclassical behavior of our optomechanical system under the fair sampling assumption.

A synopsis of this result can be found here, while the arXiv version of the paper can be found here.

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Latham Boyle, Kieran Finn, Neil Turok, CPT-Symmetric Universe, Phys. Rev. Lett., 121, 251301 (2018). (open access)

We propose that the state of the Universe does not spontaneously violate CPT. Instead, the Universe after the big bang is the CPT image of the Universe before it, both classically and quantum mechanically. The pre- and postbang epochs comprise a universe-antiuniverse pair, emerging from nothing directly into a hot, radiation-dominated era. CPT symmetry selects a unique QFT vacuum state on such a spacetime, providing a new interpretation of the cosmological baryon asymmetry, as well as a remarkably economical explanation for the cosmological dark matter. Requiring only the standard three-generation model of particle physics (with right-handed neutrinos), a ##\mathbb Z_2## symmetry suffices to render one of the right-handed neutrinos stable. We calculate its abundance from first principles: matching the observed dark matter density requires its mass to be 4.8 × 108 GeV. Several other testable predictions follow: (i) the three light neutrinos are Majorana particles and allow neutrinoless double ##\beta## decay; (ii) the lightest neutrino is massless; and (iii) there are no primordial long-wavelength gravitational waves. We mention connections to the strong CP problem and the arrow of time.
They are still working on many aspects like the CMB temperature fluctuations but testable predictions are always great. Neutrinoless double beta decay with a massless lightest neutrino is something we can potentially find in the future.
 

Wrichik Basu

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First-principles prediction of one-dimensional giant Rashba splittings in Bi-adsorbed In atomic chains

Tomonori Tanaka and Yoshihiro Gohda
Phys. Rev. B 98, 241409(R) – Published 18 December 2018

ABSTRACT

We study Bi-adsorbed In atomic chains on Si(111) in order to design a one-dimensional (1D) Rashba system using first-principles calculations. From the band dispersions and spin textures, we find that this system shows 1D giant Rashba splittings. The Rashba parameters of several structures in this system are comparable with other Rashba systems. Depending on the adsorption structure, this system also shows remarkable features such as a large out-of-plane spin polarization, the reversal of spin polarization in the Rashba bands, and a metal-insulator transition. We propose a mechanism to generate a nondissipative spin current by the gap opening due to an avoided crossing of Rashba bands. This mechanism is suitable for spintronic applications without requiring an external magnetic field.
Related news: https://www.sciencedaily.com/releases/2018/12/181227102106.htm
 

Wrichik Basu

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First Results from ABRACADABRA-10 cm: A Search for Sub-μeV Axion Dark Matter

Jonathan L. Ouellet, et. al. Physical Review Letters, March 29, 2019; DOI: 10.1103/PhysRevLett.122.121802

Abstract:
The axion is a promising dark matter candidate, which was originally proposed to solve the strong-CP problem in particle physics. To date, the available parameter space for axion and axionlike particle dark matter is relatively unexplored, particularly at masses ma≲1  μeV. ABRACADABRA is a new experimental program to search for axion dark matter over a broad range of masses, 10−12≲ma≲10−6  eV. ABRACADABRA-10 cm is a small-scale prototype for a future detector that could be sensitive to the QCD axion. In this Letter, we present the first results from a 1 month search for axions with ABRACADABRA-10 cm. We find no evidence for axionlike cosmic dark matter and set 95% C.L. upper limits on the axion-photon coupling between gaγγ<1.4×10−10 and gaγγ<3.3×10−9  GeV−1 over the mass range 3.1×10−10–8.3×10−9  eV. These results are competitive with the most stringent astrophysical constraints in this mass range.
 

Wrichik Basu

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Achievement of Reactor-Relevant Performance in Negative Triangularity Shape in the DIII-D Tokamak

M. E. Austin, A. Marinoni, M. L. Walker, M. W. Brookman, J. S. deGrassie, A. W. Hyatt, G. R. McKee, C. C. Petty, T. L. Rhodes, S. P. Smith, C. Sung, K. E. Thome, and A. D. Turnbull, Phys. Rev. Lett. 122, 115001 – Published 18 March 2019

ABSTRACT
Plasma discharges with a negative triangularity (δ=−0.4) shape have been created in the DIII-D tokamak with a significant normalized beta (βN=2.7) and confinement characteristic of the high confinement mode (H98y2=1.2) despite the absence of an edge pressure pedestal and no edge localized modes (ELMs). These inner-wall-limited plasmas have a similar global performance as a positive triangularity (δ=+0.4) ELMing H-mode discharge with the same plasma current, elongation and cross sectional area. For cases both of dominant electron cyclotron heating with Te/Ti>1 and dominant neutral beam injection heating with Te/Ti=1, turbulent fluctuations over radii 0.5<ρ<0.9 were reduced by 10–50% in the negative triangularity shape compared to the matching positive triangularity shape, depending on the radius and conditions.

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Wrichik Basu

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Single-Photon Distillation via a Photonic Parity Measurement Using Cavity QED

Severin Daiss, Stephan Welte, Bastian Hacker, Lin Li, and Gerhard Rempe
Phys. Rev. Lett. 122, 133603 – Published 5 April 2019

Abstract:
Single photons with tailored temporal profiles are a vital resource for future quantum networks. Here we distill them out of custom-shaped laser pulses that reflect from a single atom strongly coupled to an optical resonator. A subsequent measurement on the atom is employed to herald a successful distillation. Out of vacuum-dominated light pulses, we create single photons with fidelity 66(1)%, two-and-more-photon suppression 95.5(6)%, and a Wigner function with negative value −0.125(6). Our scheme applied to state-of-the-art fiber resonators could boost the single-photon fidelity to up to 96%.
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