Recent Noteworthy Physics Papers

[ZapperZ]

T.E. Collett et al., "A precise extragalactic test of General Relativity", Science v.360, p.1342 (2018).

Abstract: Einstein’s theory of gravity, General Relativity, has been precisely tested on Solar System scales, but the long-range nature of gravity is still poorly constrained. The nearby strong gravitational lens ESO 325-G004 provides a laboratory to probe the weak-field regime of gravity and measure the spatial curvature generated per unit mass, γ. By reconstructing the observed light profile of the lensed arcs and the observed spatially resolved stellar kinematics with a single self-consistent model, we conclude that γ = 0.97 ± 0.09 at 68% confidence. Our result is consistent with the prediction of 1 from General Relativity and provides a strong extragalactic constraint on the weak-field metric of gravity.

Ethan Siegel has an article describing in greater detail the significance of this result. You may read the full manuscript of the paper here.

Zz.

 

[ZapperZ]

On the heels of the previous post of GR verification at the galactic scale, comes this test of GR's strong equivalence principle involving a neutron star and two white dwarfs.

A.M. Archibald et al., "Universality of free fall from the orbital motion of a pulsar in a stellar triple system", Nature, 559, p73 (2018).

Abstract: Einstein’s theory of gravity—the general theory of relativity—is based on the universality of free fall, which specifies that all objects accelerate identically in an external gravitational field. In contrast to almost all alternative theories of gravity, the strong equivalence principle of general relativity requires universality of free fall to apply even to bodies with strong self-gravity. Direct tests of this principle using Solar System bodies are limited by the weak self-gravity of the bodies, and tests using pulsar–white-dwarf binaries have been limited by the weak gravitational pull of the Milky Way. PSR J0337+1715 is a hierarchical system of three stars (a stellar triple system) in which a binary consisting of a millisecond radio pulsar and a white dwarf in a 1.6-day orbit is itself in a 327-day orbit with another white dwarf. This system permits a test that compares how the gravitational pull of the outer white dwarf affects the pulsar, which has strong self-gravity, and the inner white dwarf. Here we report that the accelerations of the pulsar and its nearby white-dwarf companion differ fractionally by no more than 2.6 × 10⁻⁶. For a rough comparison, our limit on the strong-field Nordtvedt parameter, which measures violation of the universality of free fall, is a factor of ten smaller than that obtained from (weak-field) Solar System tests and a factor of almost a thousand smaller than that obtained from other strong-field tests.

The News and Views article on this paper can be found here.

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[ZapperZ]

These are two papers reporting on the same observation, which strengthens its validity.

The IceCube Collaboration,Fermi-LAT,MAGIC,AGILE,ASAS-SN,HAWC,H.E.S.S.,INTEGRAL,Kanata,Kiso,Kapteyn,Liverpool Telescope,Subaru,Swift/NuSTAR,VERITAS,VLA/17B-403 teams, "Multimessenger observations of a flaring blazar coincident with high-energy neutrino IceCube-170922A" Science 361, 146 (2018).

Abstract: Previous detections of individual astrophysical sources of neutrinos are limited to the Sun and the supernova 1987A, whereas the origins of the diffuse flux of high-energy cosmic neutrinos remain unidentified. On 22 September 2017, we detected a high-energy neutrino, IceCube-170922A, with an energy of ~290 tera–electron volts. Its arrival direction was consistent with the location of a known γ-ray blazar, TXS 0506+056, observed to be in a flaring state. An extensive multiwavelength campaign followed, ranging from radio frequencies to γ-rays. These observations characterize the variability and energetics of the blazar and include the detection of TXS 0506+056 in very-high-energy γ-rays. This observation of a neutrino in spatial coincidence with a γ-ray–emitting blazar during an active phase suggests that blazars may be a source of high-energy neutrinos.

Full paper can be found here.The IceCube Collaboration, "Neutrino emission from the direction of the blazar TXS 0506+056 prior to the IceCube-170922A alert" Science 361, 147 (2018)

Abstract: A high-energy neutrino event detected by IceCube on 22 September 2017 was coincident in direction and time with a gamma-ray flare from the blazar TXS 0506+056. Prompted by this association, we investigated 9.5 years of IceCube neutrino observations to search for excess emission at the position of the blazar. We found an excess of high-energy neutrino events, with respect to atmospheric backgrounds, at that position between September 2014 and March 2015. Allowing for time-variable flux, this constitutes 3.5σ evidence for neutrino emission from the direction of TXS 0506+056, independent of and prior to the 2017 flaring episode. This suggests that blazars are identifiable sources of the high-energy astrophysical neutrino flux.

Full paper can be found here.

These two papers are significant because it adds another "messenger", this time neutrinos, in making astronomical observation. We had light/EM radiation since the beginning of observational astronomy, and we recently added gravitational waves to that. So welcome, neutrinos!

Zz.

 

[mfb]

Based on an ESA mission:
Radar evidence of subglacial liquid water on Mars

The presence of liquid water at the base of the martian polar caps has long been suspected but not observed. We surveyed the Planum Australe region using the MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) instrument, a low-frequency radar on the Mars Express spacecraft . Radar profiles collected between May 2012 and December 2015 contain evidence of liquid water trapped below the ice of the South Polar Layered Deposits. Anomalously bright subsurface reflections are evident within a well-defined, 20-kilometer-wide zone centered at 193°E, 81°S, which is surrounded by much less reflective areas. Quantitative analysis of the radar signals shows that this bright feature has high relative dielectric permittivity (>15), matching that of water-bearing materials. We interpret this feature as a stable body of liquid water on Mars.

Needs verification, especially from an upcoming Chinese spacecraft , but it is a very interesting signature.

 

[mfb]

Based on ESO's Very Large Telescope: The first measurement of gravitational redshift of a star orbiting a supermassive black hole.

Detection of the gravitational redshift in the orbit of the star S2 near the Galactic centre massive black hole

The highly elliptical, 16-year-period orbit of the star S2 around the massive black hole candidate Sgr A✻ is a sensitive probe of the gravitational field in the Galactic centre. Near pericentre at 120 AU ≈ 1400 Schwarzschild radii, the star has an orbital speed of ≈7650 km s⁻¹, such that the first-order effects of Special and General Relativity have now become detectable with current capabilities. Over the past 26 years, we have monitored the radial velocity and motion on the sky of S2, mainly with the SINFONI and NACO adaptive optics instruments on the ESO Very Large Telescope, and since 2016 and leading up to the pericentre approach in May 2018, with the four-telescope interferometric beam-combiner instrument GRAVITY. From data up to and including pericentre, we robustly detect the combined gravitational redshift and relativistic transverse Doppler effect for S2 of z = Δλ / λ ≈ 200 km s−1/c with different statistical analysis methods. When parameterising the post-Newtonian contribution from these effects by a factor f , with f = 0 and f = 1 corresponding to the Newtonian and general relativistic limits, respectively, we find from posterior fitting with different weighting schemes f = 0.90 ± 0.09_stat ± 0.15_sys. The S2 data are inconsistent with pure Newtonian dynamics.

 

[Deepblu]

Furey, SU(3)xSU(2)xU(1) (xU(1)) as a symmetry of division algebraic ladder operators, Eur. Phys. J. C (2018)

https://arxiv.org/abs/1806.00612

 

[ZapperZ]

Please make sure you read the very first post. Try to keep the format that we have been using in this thread.

Zz.

 

[Andy Resnick]

Quis custodiet ipsos custodes? (Who watches the watchers?):

Quantum theory cannot consistently describe the use of itself

Abstract:
Quantum theory provides an extremely accurate description of fundamental processes in physics. It thus seems likely that the theory is applicable beyond the, mostly microscopic, domain in which it has been tested experimentally. Here, we propose a Gedankenexperiment to investigate the question whether quantum theory can, in principle, have universal validity. The idea is that, if the answer was yes, it must be possible to employ quantum theory to model complex systems that include agents who are themselves using quantum theory. Analysing the experiment under this presumption, we find that one agent, upon observing a particular measurement outcome, must conclude that another agent has predicted the opposite outcome with certainty. The agents’ conclusions, although all derived within quantum theory, are thus inconsistent. This indicates that quantum theory cannot be extrapolated to complex systems, at least not in a straightforward manner.

 

[DrClaude]

Quis custodiet ipsos custodes? (Who watches the watchers?):

Quantum theory cannot consistently describe the use of itself

Note that there is a thread discussing that paper: https://www.physicsforums.com/threads/quantum-theory-nature-paper-18-sept.955748/

 

[mfb]

A possible explanation how supermassive black holes could grow so quickly in the early universe: Misaligned accretion disks.

An ultrafast inflow in the luminous Seyfert PG1211+143
K A Pounds, C J Nixon, A Lobban, A R King
Monthly Notices of the Royal Astronomical Society, Volume 481, Issue 2, 1 December 2018, Pages 1832–1838, https://doi.org/10.1093/mnras/sty2359

Blueshifted absorption lines in the X-ray spectra of an active galactic nucleus (AGN) show that ultrafast outflows with typical velocities v∼ 0.1c are a common feature of these luminous objects. Such powerful AGN winds offer an explanation of the observed M–σ relation linking the mass of the supermassive black hole and the velocity dispersion in the galaxy’s stellar bulge. An extended XMM–Newton study of the luminous Seyfert galaxy PG1211+143 recently revealed a variable multivelocity wind. Here we report the detection of a short-lived, ultrafast inflow during the same observation. Previous reports of inflows used single absorption lines with uncertain identifications, but this new result identifies an array of resonance absorption lines of highly ionized Fe, Ca, Ar, S, and Si, sharing a common redshift when compared with a grid of realistic photoionization spectra. The redshifted absorption arises in a column of highly ionized matter close to the black hole, with a line-of-sight velocity, v∼ 0.3c, inconsistent with the standard picture of a plane circular accretion disc. This may represent the first direct evidence for chaotic accretion in an AGN, where accretion discs are generally misaligned to the black hole spin. For sufficient inclinations, the Lense–Thirring effect can break the discs into discrete rings, which then precess, collide, and shock, causing near free-fall of gas towards the black hole. The observed accretion rate for the reported infall is comparable to the hard X-ray luminosity in PG1211+143, suggesting that direct infall may be a significant contributor to inner disc accretion.

 

[ZapperZ]

Again, please follow the format set in the First Post. While links are welcomed, we have seen how those can disappear or become broken. So please include all the proper citations as indicated in the post itself (Authors, Title, Journal info, Year).

Zz.

 

[mfb]

Black holes larger than 0.01 solar masses are not a large contribution to dark matter, based on an analysis of supernova lensing.

Limits on Stellar-Mass Compact Objects as Dark Matter from Gravitational Lensing of Type Ia Supernovae
Miguel Zumalacárregui and Uroš Seljak, Phys. Rev. Lett. 121, 141101

The nature of dark matter (DM) remains unknown despite very precise knowledge of its abundance in the Universe. An alternative to new elementary particles postulates DM as made of macroscopic compact halo objects (MACHO) such as black holes formed in the very early Universe. Stellar-mass primordial black holes (PBHs) are subject to less robust constraints than other mass ranges and might be connected to gravitational-wave signals detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO). New methods are therefore necessary to constrain the viability of compact objects as a DM candidate. Here we report bounds on the abundance of compact objects from gravitational lensing of type Ia supernovae (SNe). Current SNe data sets constrain compact objects to represent less than 35.2% (Joint Lightcurve Analysis) and 37.2% (Union 2.1) of the total matter content in the Universe, at 95% confidence level. The results are valid for masses larger than ∼0.01 M_⊙ (solar masses), limited by the size SNe relative to the lens Einstein radius. We demonstrate the mass range of the constraints by computing magnification probabilities for realistic SNe sizes and different values of the PBH mass. Our bounds are sensitive to the total abundance of compact objects with M≳0.01 M_⊙ and complementary to other observational tests. These results are robust against cosmological parameters, outlier rejection, correlated noise, and selection bias. PBHs and other MACHOs are therefore ruled out as the dominant form of DM for objects associated to LIGO gravitational wave detections. These bounds constrain early-Universe models that predict stellar-mass PBH production and strengthen the case for lighter forms of DM, including new elementary particles.

Extending this to a larger set of supernovae leads to stricter limits of 0.23, but that hasn't been published yet.

 

[ZapperZ]

ACME Collaboration, "Improved limit on the electric dipole moment of the electron", Nature 562, p355 (2018).

Abstract: The standard model of particle physics accurately describes all particle physics measurements made so far in the laboratory. However, it is unable to answer many questions that arise from cosmological observations, such as the nature of dark matter and why matter dominates over antimatter throughout the Universe. Theories that contain particles and interactions beyond the standard model, such as models that incorporate supersymmetry, may explain these phenomena. Such particles appear in the vacuum and interact with common particles to modify their properties. For example, the existence of very massive particles whose interactions violate time-reversal symmetry, which could explain the cosmological matter–antimatter asymmetry, can give rise to an electric dipole moment along the spin axis of the electron. No electric dipole moments of fundamental particles have been observed. However, dipole moments only slightly smaller than the current experimental bounds have been predicted to arise from particles more massive than any known to exist. Here we present an improved experimental limit on the electric dipole moment of the electron, obtained by measuring the electron spin precession in a superposition of quantum states of electrons subjected to a huge intramolecular electric field. The sensitivity of our measurement is more than one order of magnitude better than any previous measurement. This result implies that a broad class of conjectured particles, if they exist and time-reversal symmetry is maximally violated, have masses that greatly exceed what can be measured directly at the Large Hadron Collider.

You might be able to access the full paper here: https://www.nature.com/articles/s41586-018-0599-8.epdf?referrer_access_token=vmq0MmYkAgwoWvTRTILeHtRgN0jAjWel9jnR3ZoTv0PfAsJPWCr3ZaUcxY33i4Ut_fU7xhmKu7oeslGzYzVDTT8da13IcRaySq4SXrdLcVFa5HIwBNoOWEmuUEdQFonhHaS3B1huHRs8W_p2wGadL3yEzzJXS_l6AeNZw8V9IVScPbeNAPJFt7tpxHBu9NH2Hsiyxzh5HTa7uDXFOGwa8KouXQfPIQHWb6sp86xaN4DHN3uy9-9eGrl63AUEhxUjHQuv0pmAXgLy7p7qbRYcHA==&tracking_referrer=www.sciencenews.org

A review of this result can be found here: https://www.sciencenews.org/article/electron-shape-round-standard-model-physics

Zz.

 

[DennisN]

Isn't it time we had a paper about thermodynamics and experiments in the thread? If it's hot or not, I leave up to the reader...

Jaehoon Bang, Rui Pan et al., "Experimental realization of Feynman's ratchet", New Journal of Physics, Volume 20, October 2018

The paper can be read online here: http://iopscience.iop.org/article/10.1088/1367-2630/aae71f/meta
Link to a pdf of the paper: http://iopscience.iop.org/article/10.1088/1367-2630/aae71f/pdf

Abstract: Feynman's ratchet is a microscopic machine in contact with two heat reservoirs, at temperatures T_A and T_B , that was proposed by Richard Feynman to illustrate the second law of thermodynamics. In equilibrium (T_A = T_B), thermal fluctuations prevent the ratchet from generating directed motion. When the ratchet is maintained away from equilibrium by a temperature difference (T_A ≠ T_B), it can operate as a heat engine, rectifying thermal fluctuations to perform work. While it has attracted much interest, the operation of Feynman's ratchet as a heat engine has not been realized experimentally, due to technical challenges. In this work, we realize Feynman's ratchet with a colloidal particle in a one-dimensional optical trap in contact with two heat reservoirs: one is the surrounding water, while the effect of the other reservoir is generated by a novel feedback mechanism, using the Metropolis algorithm to impose detailed balance. We verify that the system does not produce work when T_A = T_B , and that it becomes a microscopic heat engine when T_A ≠ T_B. We analyze work, heat and entropy production as functions of the temperature difference and external load. Our experimental realization of Feynman's ratchet and the Metropolis algorithm can also be used to study the thermodynamics of feedback control and information processing, the working mechanism of molecular motors, and controllable particle transportation.

 

[mfb]

Entanglement between living bacteria and quantized light witnessed by Rabi splitting

C Marletto et al., Journal of Physics Communications, Volume 2, Number 10

We model recent experiments on living sulphur bacteria interacting with quantised light, using the Dicke model. Our analysis shows that the strong coupling between the bacteria and the light, when both are treated quantum-mechanically, indicates that in those experiments there is entanglement between the bacteria (modelled as dipoles) and the quantised light (modelled as a single quantum harmonic oscillator). The existence of lower polariton branch due to the vacuum Rabi splitting, measured in those experiments for a range of different parameters, ensures the negativity of energy (with respect to the lowest energy of separable states), thus acting as an entanglement witness.

 

[ZapperZ]

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.

Zz.

 

[mfb]

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]

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]

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]

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.

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.115001
Related discussion:
https://www.physicsforums.com/threads/new-tokamak-d-mode-success-fusion-is-almost-here.968614/

 

[Wrichik Basu]

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%.

https://doi.org/10.1103/PhysRevLett.122.133603

 

[Wrichik Basu]

Observation of Atom Number Fluctuations in a Bose-Einstein Condensate

M. A. Kristensen, M. B. Christensen, M. Gajdacz, M. Iglicki, K. Pawłowski, C. Klempt, J. F. Sherson, K. Rzążewski, A. J. Hilliard, and J. J. Arlt
Phys. Rev. Lett. 122, 163601 – Published 22 April 2019

Abstract:

Fluctuations are a key property of both classical and quantum systems. While the fluctuations are well understood for many quantum systems at zero temperature, the case of an interacting quantum system at finite temperature still poses numerous challenges. Despite intense theoretical investigations of atom number fluctuations in Bose-Einstein condensates, their amplitude in experimentally relevant interacting systems is still not fully understood. Moreover, technical limitations have prevented their experimental investigation to date. Here we report the observation of these fluctuations. Our experiments are based on a stabilization technique, which allows for the preparation of ultracold thermal clouds at the shot noise level, thereby eliminating numerous technical noise sources. Furthermore, we make use of the correlations established by the evaporative cooling process to precisely determine the fluctuations and the sample temperature. This allows us to observe a telltale signature: the sudden increase in fluctuations of the condensate atom number close to the critical temperature.

https://doi.org/10.1103/PhysRevLett.122.163601

 

[Wrichik Basu]

Cherenkov Radiation from the Quantum Vacuum (Open Access)

Alexander J. Macleod, Adam Noble, and Dino A. Jaroszynski
Phys. Rev. Lett. 122, 161601 – Published 24 April 2019

Abstract:

A charged particle moving through a medium emits Cherenkov radiation when its velocity exceeds the phase velocity of light in that medium. Under the influence of a strong electromagnetic field, quantum fluctuations can become polarized, imbuing the vacuum with an effective anisotropic refractive index and allowing the possibility of Cherenkov radiation from the quantum vacuum. We analyze the properties of this vacuum Cherenkov radiation in strong laser pulses and the magnetic field around a pulsar, finding regimes in which it is the dominant radiation mechanism. This radiation process may be relevant to the excess signals of high energy photons in astrophysical observations.

https://doi.org/10.1103/PhysRevLett.122.161601

 

[Wrichik Basu]

Imaging individual barium atoms in solid xenon for barium tagging in nEXO

T. Walton et. al., Nature volume 569, pages203–207 (2019)

Abstract:

Double-β-decay involves the simultaneous conversion of two neutrons into two protons, and the emission of two electrons and two neutrinos; the neutrinoless process, although not yet observed, is thought to involve the emission of the two electrons but no neutrinos. The search for neutrinoless-double-β-decay probes fundamental properties of neutrinos, including whether or not the neutrino and antineutrino are distinct particles. Double-β-decay detectors are large and expensive, so it is essential to achieve the highest possible sensitivity with each study, and removing spurious contributions (‘background’) from detected signals is crucial. In the nEXO neutrinoless-double-β-decay experiment, the identification, or ‘tagging’, of the ¹³⁶Ba daughter atom resulting from the double-β decay of ¹³⁶Xe provides a technique for discriminating background. The tagging scheme studied here uses a cryogenic probe to trap the barium atom in a solid xenon matrix, where the barium atom is tagged through fluorescence imaging. Here we demonstrate the imaging and counting of individual barium atoms in solid xenon by scanning a focused laser across a solid xenon matrix deposited on a sapphire window. When the laser irradiates an individual atom, the fluorescence persists for about 30 seconds before dropping abruptly to the background level—a clear confirmation of one-atom imaging. Following evaporation of a barium deposit, the residual barium fluorescence is 0.16 per cent or less. Our technique achieves the imaging of single atoms in a solid noble element, establishing the basic principle of barium tagging for nEXO.

https://doi.org/10.1038/s41586-019-1169-4
https://www.nature.com/articles/s41586-019-1169-4
Related news:
https://www.sciencedaily.com/releases/2019/04/190429111856.htm

 

[Wrichik Basu]

Ion-Based Quantum Sensor for Optical Cavity Photon Numbers

Moonjoo Lee, Konstantin Friebe, Dario A. Fioretto, Klemens Schüppert, Florian R. Ong, David Plankensteiner, Valentin Torggler, Helmut Ritsch, Rainer Blatt, and Tracy E. Northup
Phys. Rev. Lett. 122, 153603 – Published 19 April 2019

Abstract:

We dispersively couple a single trapped ion to an optical cavity to extract information about the cavity photon-number distribution in a nondestructive way. The photon-number-dependent ac Stark shift experienced by the ion is measured via Ramsey spectroscopy. We use these measurements first to obtain the ion-cavity interaction strength. Next, we reconstruct the cavity photon-number distribution for coherent states and for a state with mixed thermal-coherent statistics, finding overlaps above 99% with the calibrated states.

https://doi.org/10.1103/PhysRevLett.122.153603

 

[Wrichik Basu]

Observation of the Nuclear Barnett Effect

Mohsen Arabgol and Tycho Sleator
Phys. Rev. Lett. 122, 177202 – Published 2 May 2019

Abstract:

We have made the first observation of the nuclear Barnett effect. In the electronic Barnett effect, which was first observed in 1915 by Samuel Barnett, a ferromagnetic rod was spun about its long axis and a magnetization developed in the rod along the axis of rotation. This effect is caused by the coupling between the angular momentum of the electronic spins in the sample and the rotational motion of the rod. In our experiment, we measured the nuclear Barnett effect by rotating a sample of water at rotational speeds up to 13.5 kHz in a weak magnetic field and observed a change in the polarization of the protons in the sample that is proportional to the frequency of rotation. We measured this polarization by observing the change in the size of a nuclear magnetic resonance (NMR) signal. No NMR frequency shift was observed due to rotation, meaning that this magnetization was not produced by a real magnetic field.

https://doi.org/10.1103/PhysRevLett.122.177202

 

[Wrichik Basu]

Liquid Helix: How Capillary Jets Adhere to Vertical Cylinders

E. Jambon-Puillet, W. Bouwhuis, J. H. Snoeijer, and D. Bonn
Phys. Rev. Lett. 122, 184501 – Published 8 May 2019

Abstract:

From everyday experience, we all know that a solid edge can deflect a liquid flowing over it significantly, up to the point where the liquid completely sticks to the solid. Although important in pouring, printing, and extrusion processes, there is no predictive model of this so-called “teapot effect.” By grazing vertical cylinders with inclined capillary liquid jets, here we use the teapot effect to attach the jet to the solid and form a new structure: the liquid helix. Using mass and momentum conservation along the liquid stream, we first quantitatively predict the shape of the helix and then provide a parameter-free inertial-capillary adhesion model for the jet deflection and critical velocity for helix formation.

https://doi.org/10.1103/PhysRevLett.122.184501

 

[Wrichik Basu]

Fidelity benchmarks for two-qubit gates in silicon

W. Huang, C. H. Yang, K. W. Chan, T. Tanttu, B. Hensen, R. C. C. Leon, M. A. Fogarty, J. C. C. Hwang, F. E. Hudson, K. M. Itoh, A. Morello, A. Laucht, A. S. Dzurak, Nature 2019.

Universal quantum computation will require qubit technology based on a scalable platform, together with quantum error correction protocols that place strict limits on the maximum infidelities for one- and two-qubit gate operations. Although various qubit systems have shown high fidelities at the one-qubit level, the only solid-state qubits manufactured using standard lithographic techniques that have demonstrated two-qubit fidelities near the fault-tolerance threshold have been in superconductor systems. Silicon-based quantum dot qubits are also amenable to large-scale fabrication and can achieve high single-qubit gate fidelities (exceeding 99.9 per cent) using isotopically enriched silicon. Two-qubit gates have now been demonstrated in a number of systems, but as yet an accurate assessment of their fidelities using Clifford-based randomized benchmarking, which uses sequences of randomly chosen gates to measure the error, has not been achieved. Here, for qubits encoded on the electron spin states of gate-defined quantum dots, we demonstrate Bell state tomography with fidelities ranging from 80 to 89 per cent, and two-qubit randomized benchmarking with an average Clifford gate fidelity of 94.7 per cent and an average controlled-rotation fidelity of 98 per cent. These fidelities are found to be limited by the relatively long gate times used here compared with the decoherence times of the qubits. Silicon qubit designs employing fast gate operations with high Rabi frequencies, together with advanced pulsing techniques, should therefore enable much higher fidelities in the near future.

https://doi.org/10.1038/s41586-019-1197-0Related news:
https://www.sciencedaily.com/releases/2019/05/190513112223.htm

 

[Wrichik Basu]

Demonstration of Displacement Sensing of a mg-Scale Pendulum for mm- and mg-Scale Gravity Measurements

Nobuyuki Matsumoto, Seth B. Cataño-Lopez, Masakazu Sugawara, Seiya Suzuki, Naofumi Abe, Kentaro Komori, Yuta Michimura, Yoichi Aso, and Keiichi Edamatsu
Phys. Rev. Lett. 122, 071101 – Published 19 February 2019

Gravity generated by large masses has been observed using a variety of probes from atomic interferometers to torsional balances. However, gravitational coupling between small masses has never been observed so far. Here, we demonstrate sensitive displacement sensing of the Brownian motion of an optically trapped 7 mg pendulum motion whose natural quality factor is increased to 10⁸ through dissipation dilution. The sensitivity for an integration time of one second corresponds to the displacement generated in a millimeter-scale gravitational experiment between the probe and a 100 mg source mass, whose position is modulated at the pendulum mechanical resonant frequency. Development of such a sensitive displacement sensor using a milligram-scale device will pave the way for a new class of experiments where gravitational coupling between small masses in quantum regimes can be achieved.

https://doi.org/10.1103/PhysRevLett.122.071101

 

[Wrichik Basu]

Anomalous dispersion of microcavity trion-polaritons

S. Dhara et. al. Nature Physics volume 14, pages130–133 (2018)

The strong coupling of excitons to optical cavities has provided new insights into cavity quantum electrodynamics as well as opportunities to engineer nanoscale light–matter interactions. Here we study the interaction between out-of-equilibrium cavity photons and both neutral and negatively charged excitons, by embedding a single layer of the atomically thin semiconductor molybdenum diselenide in a monolithic optical cavity based on distributed Bragg reflectors. The interactions lead to multiple cavity polariton resonances and anomalous band inversion for the lower, trion-derived, polariton branch—the central result of the present work. Our theoretical analysis reveals that many-body effects in an out-of-equilibrium setting result in an effective level attraction between the exciton-polariton and trion-polariton accounting for the experimentally observed inverted trion-polariton dispersion. Our results suggest a pathway for studying interesting regimes in quantum many-body physics yielding possible new phases of quantum matter as well as fresh possibilities for polaritonic device architectures.

https://doi.org/10.1038/nphys4303

 

[Wrichik Basu]

Superconductivity at 250 K in lanthanum hydride under high pressures

A. P. Drozdov et al. Nature 569, 528–531 (2019)

With the discovery of superconductivity at 203 kelvin in H3S, attention returned to conventional superconductors with properties that can be described by the Bardeen–Cooper–Schrieffer and the Migdal–Eliashberg theories. Although these theories predict the possibility of room-temperature superconductivity in metals that have certain favourable properties—such as lattice vibrations at high frequencies—they are not sufficient to guide the design or predict the properties of new superconducting materials. First-principles calculations based on density functional theory have enabled such predictions, and have suggested a new family of superconducting hydrides that possesses a clathrate-like structure in which the host atom (calcium, yttrium, lanthanum) is at the centre of a cage formed by hydrogen atoms. For LaH10 and YH10, the onset of superconductivity is predicted to occur at critical temperatures between 240 and 320 kelvin at megabar pressures. Here we report superconductivity with a critical temperature of around 250 kelvin within the $Fm3m$ structure of LaH10 at a pressure of about 170 gigapascals. This is, to our knowledge, the highest critical temperature that has been confirmed so far in a superconducting material. Superconductivity was evidenced by the observation of zero resistance, an isotope effect, and a decrease in critical temperature under an external magnetic field, which suggested an upper critical magnetic field of about 136 tesla at zero temperature. The increase of around 50 kelvin compared with the previous highest critical temperature1 is an encouraging step towards the goal of achieving room-temperature superconductivity in the near future.

https://doi.org/10.1038/s41586-019-1201-8

 

[DennisN]

I think this was pretty nice... ...and I include an open access arxiv link below, and an article about it.

Philip Willke, Kai Yang et al., Magnetic resonance imaging of single atoms on a surface, Nature Physics (2019)
Published: 01 July 2019

Magnetic resonance imaging (MRI) revolutionized diagnostic medicine and biomedical research by allowing non-invasive access to spin ensembles. To enhance MRI resolution to the nanometre scale, new approaches including scanning probe methods have been used in recent years, which culminated in the detection of individual spins. This allowed for the visualization of organic samples and magnetic structures as well as identifying the location of electron and nuclear spins. Here, we demonstrate the MRI of individual atoms on a surface. The set-up, implemented in a cryogenic scanning tunnelling microscope, uses single-atom electron spin resonance to achieve subångström resolution, exceeding the spatial resolution of previous MRI experiments by one to two orders of magnitude. We find that MRI scans of different atomic species and with different probe tips lead to unique signatures in the resonance images. These signatures reveal the magnetic interactions between the tip and the atom, in particular magnetic dipolar and exchange interaction.

Paper in Nature Physics: http://www.nature.com/articles/s41567-019-0573-x
Paper on arxiv: http://arxiv.org/abs/1807.08944
Article: World's smallest MRI performed on single atoms (nanowerk)

 

[mfb]

Detection and counting of individual phonons:

L. R. Sletten, B. A. Moores, J. J. Viennot, and K. W. Lehnert, Phys. Rev. X 9, 021056
Resolving Phonon Fock States in a Multimode Cavity with a Double-Slit Qubit
arXiv version

Edit: Has its own discussion thread now

We resolve phonon number states in the spectrum of a superconducting qubit coupled to a multimode acoustic cavity. Crucial to this resolution is the sharp frequency dependence in the qubit-phonon interaction engineered by coupling the qubit to surface acoustic waves in two locations separated by ∼40 acoustic wavelengths. In analogy to double-slit diffraction, the resulting interference generates high-contrast frequency structure in the qubit-phonon interaction. We observe this frequency structure both in the coupling rate to multiple cavity modes and in the qubit spontaneous emission rate into unconfined modes. We use this sharp frequency structure to resolve single phonons by tuning the qubit to a frequency of destructive interference where all acoustic interactions are dispersive. By exciting several detuned yet strongly coupled phononic modes and measuring the resulting qubit spectrum, we observe that, for two modes, the device enters the strong dispersive regime where single phonons are spectrally resolved.

 

[Wrichik Basu]

Validation of energy deposition simulations for proton and heavy ion losses in the CERN Large Hadron Collider

A. Lechner et. al.

Phys. Rev. Accel. Beams 22, 071003 – Published 11 July 2019

Monte Carlo shower simulations are essential for understanding and predicting the consequences of beam losses in high-energy proton and ion colliders. Shower simulations are routinely used at CERN for estimating the beam-induced energy deposition, radiation damage, and radioactivity in the Large Hadron Collider (LHC). Comparing these shower simulations against beam loss measurements is an important prerequisite for assessing the predictive ability of model calculations. This paper validates fluka simulation predictions of beam loss monitor (BLM) signals against BLM measurements from proton fills at $3.5$ and $4\,TeV$ and $^{208}Pb^{82+}$ ion fills at $1.38A\, TeV$. The paper addresses typical loss scenarios and loss mechanisms encountered in LHC operation, including proton collisions with dust particles liberated into the beams, halo impact on collimators in the betatron cleaning insertion, proton-proton collisions in the interaction points, and dispersive losses due to bound-free pair production in heavy ion collisions. Model predictions and measured signals generally match within a few tens of percent, although systematic differences were found to be as high as a factor of 3 for some regions and source terms.

https://doi.org/10.1103/PhysRevAccelBeams.22.071003

 

[mfb]

@Wrichik Basu: That looks like one out of hundreds of detector studies to me.

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Krzysztof A. Meissner and Hermann Nicolai propose Planck-mass gravitinos as dark matter candidates. They get stability from fractional quantized electric charge and they might have some color charge. With their heavy mass they must be rare but they could lead to characteristic signatures in crystals they pass through.

An earlier paper:
Standard Model Fermions and Infinite-Dimensional R Symmetries, Phys. Rev. Lett. 121, 091601

Following up on our earlier work [K. A. Meissner and H. Nicolai, Phys. Rev. D 91, 065029 (2015)] where we showed how to amend a scheme originally proposed by M. Gell-Mann to identify the 48 spin-12 fermions of N=8 supergravity that remain after complete breaking of N=8 supersymmetry with the 3×16 quarks and leptons of the standard model, we further generalize the construction to account for the full SU(3)_c×SU(2)_w×U(1)_Y assignments, with an additional family symmetry SU(3)_f. Our proposal relies in an essential way on embedding the SU(8) R symmetry of N=8 supergravity into the (infinite-dimensional) “maximal compact” subgroup K(E₁₀) of the conjectured maximal duality symmetry E₁₀. As a by-product, it predicts fractionally charged and possibly strongly interacting massive gravitinos. It also indicates how E₁₀ and K(E₁₀) can supersede supersymmetry as a guiding principle for unification

A recent paper discussing consistency with cosmology and experimental signatures:
Planck mass charged gravitino dark matter, Phys. Rev. D 100, 035001

Following up on our earlier work predicting fractionally charged supermassive gravitinos, we explain their potential relevance as novel candidates for dark matter and discuss possible signatures and ways to detect them.