 |
RSS feeds |
|
|||||
| Issue 12, 2024 |
|
||||||
|
|
|
||||||
Extracts from the Internet | ||
Observation of β-phase of superfluid helium-31 February 2022V.V. Dmitriev (P.L. Kapitza IPP RAS) and his co-authors were the first to carry out observation of β-phase of superfluid 3He in nematic aerogel in a strong magnetic field [1]. Under ordinary conditions, superfluid 3He has only two phases (A and B). In a strong magnetic field, however, it splits into new phases with different spin compositions of the ensemble of Cooper pairs. If, in addition, 3He is confined in nematic aerogel (loose medium of siliceous filaments or another substance) with co-directed filaments, then a strong anisotropy and a polar phase may appear. E.V. Surovtsev (IPP RAS and MIPT) predicted [2, 3] that under such conditions 3He, when cooled, will transfer into the so-called β-phase instead of the purely polar phase, and then to a deformed β-phase with a further cooling. Used in the new experiment was nematic aerogel of mullite (a mineral of the silicate class) with elongated pores, in which solid 3He layers on the filament surface were replaces by 4He. The aerogel was fixed at a mechanical cavity, and the resonance properties of this system as a function of temperature were examined. Transition of 3He into one or another phase was accompanied by a change in the superfluid component density and thus affected the resonant frequency and the shape of the resonance curve. This method was used to register the predicted transitions to a superfluid β-phase and a deformed β-phase. The temperature range of β-phase was found to be proportional to the magnetic field value. For superfluid β-phases in aerogel, see also [4]. [1] Dmitriev V V, Kutuzov M S, Soldatov A A, Yudin A N Phys. Rev. Lett. 127 265301 (2021) [2] E.V. Surovtsev, J. Exp. Theor. Phys. 128 477 (2019) [3] E.V. Surovtsev, J. Exp. Theor. Phys. 129 1055 (2019) [4] Dmitriev V V, Zav’yalov V V, Zmeev D E, Kosarev I V Phys. Usp. 46 438 (2003); UFN 173 452 (2003) Casimir effect and the non-reciprocal energy transfer1 February 2022Z. Xu (Perdue University, USA) and their co-authors performed an experiment demonstrating for the first time a non-reciprocal energy transfer from one micromechanical oscillator to another [6] via Casimir effect (see [5]). The oscillators were made of two rods with different resonant frequencies of elastic mechanical vibrations. In the region between the rods, zero electromagnetic-field vacuum fluctuations (the Casimir effect) took place that generated rod-affecting forces. An alternating electric field excited parametric modulations of the distance between the rods and the Casimir forces, thus favoring rod vibration coupling. An additional energy dissipation was artificially induced in one of the rods (energy receiver), thus leading to the occurrence of an exceptional point in the parameter space. This point is the boundary of the presence of real values in the spectrum of the Hamiltonian containing non-Hermitian terms. In bypassing the loop in the parameter space, more energy was transferred from one rod to the other than in the reverse direction, like in the case of electric current running through a diode. This effect may find useful applications in micromechanical systems. [5] Mostepanenko V M, Trunov N N Sov. Phys. Usp. 31 965 (1988); UFN 156 385 (1988) [6] Xu Z et al. Non-reciprocal energy transfer through the Casimir effect, Nature Nanotechnology (2021) Quantum teleportation of microwaves1 February 2022An important role for construction of quantum computers is played by quantum coherent transmission of states between spaced facilities such as quantum processors. It is desirable to transmit unknown quantum states through quantum teleportation. However, as distinct from the optical range, propagating quantum states were not earlier transmitted between superconducting cells in the microwave frequency range. K.G. Fedorov (Walter Meissner Institute of the Bavarian Academy of Sciences and Technical University of Munich, Germany) experimentally demonstrated quantum teleportation of propagating microwave states at a distance of 42 cm through a coaxial cable at a carrier frequency of 5.435 GHz by a preliminary squeezing and entanglement of photon states in two Josephson parametric amplifiers [7]. An analogous pair of amplifiers was employed for measurements on the side of recipient using Wigner quantum tomography of states. Quantum fidelity of teleportation F=0.689±0.004 was reached, exceeding the asymptotic quantum-state no-cloning threshold of 2/3. Teleportation of subsequent states (alphabet) was also demonstrated in the experiment. This result opens new possibilities of creating quantum microwave circuits for quantum communication and distributed quantum calculations. For quantum computers, see [8-10]. [7] Fedorov K G et al. Science Advances 7(52) (2021) [8] Sukachev D D Phys. Usp. 64 1021 (2021); UFN 191 1077 (2021) [9] Arbekov I M, Molotkov S N Phys. Usp. 64 617 (2021); UFN 191 651 (2021) [10] Trushechkin A S, Kiktenko E O, Kronberg D A, Fedorov A K Phys. Usp. 64 88 (2021); UFN 191 93 (2021) Twisted NOON states of photons1 February 2022NOON states are a superposition of N photons in two orthogonal modes (|N,0⟩ +|0,N⟩)/√2. A change in the NOON phase under external action is N times larger than in one-photon states, and therefore such states are interesting in metrological and other applications. A group of scientists from Finland and Canada have performed a new experiment [11] combining the advantage of NOON states and the possibilities of “twisted” states with orbital angular momenta. This allowed obtaining, along with the sensitivity to phase variations, a high sensitivity in angular measurements. First, two quantum entangled photons passed through different regions of a spatial modulator. Then, the structured photons met again in a splitter and got into a second modulator, which imitated the measured system. Finally, the photons were transmitted through a Mach-Zehnder interferometer and were registered. Photon states with N=1 and 2 and with orbital angular momenta up to 100h/(2π) were used. Measurements have shown that an increase of N and the orbital angular momentum heightens precision of angular measurements and detector sensitivity as was theoretically predicted. [11] Hiekkamäki M, Bouchard F, Fickler R Phys. Rev. Lett. 127 263601 (2021) The double pulsar and a test of the General Relativity Theory1 February 2022The long-term observations of the double radio pulsar PSR J0737-3039A/B with several telescopes made it possible to perform a new test of the General Relativity Theory (GRT) predictions in the region of strong fields [12]. Neutron stars form a pair with a sufficiently short orbital period of 2.45 h, their orbit has a nonzero eccentricity e=0.088, and the orbit plane is optimally oriented with respect to the line of sight. This makes the double pulsar PSR J0737-3039A/B a convenient system for testing some relativistic effects. The pulse arrival time containing information about the properties of pulsars and their gravitational field was measured using an atomic clock. Seven relativistic post-Keplerian corrections were measured. Some relativistic effects were revealed for the first time. The deviation of pulses in the gravitational field of the companion was registered, which allowed the pulsar rotation direction to be determined. Observed was the orbit variation owing to the effective pulsar mass loss due to pulsar rotation retardation. The angular velocity of periastron rotation was measured. The current accuracy already makes it possible to see the influence of the equation of state of the neutron star on the spin-orbital coupling in the binary system. The orbit period variation rate due to gravitational wave radiation corresponds to the formulas for quadrupole approximation to an accuracy of 1.3×10−4. Thus, the GRT predictions have been confirmed once again and some alternative gravitational theories constrained. For radio pulsars, see [13, 14]. [12] Kramer M et al. Phys. Rev. X 11 041050 (2021) [13] Beskin V S Phys. Usp. 61 353 (2018); UFN 188 377 (2018) [14] Beskin V S, Istomin Ya N, Philippov A A Phys. Usp. 56 164 (2013); UFN 183 179 (2013) |
The Extracts from the Internet is a section of Uspekhi Fizicheskih Nauk (Physics Uspekhi) — the monthly rewiew journal of the current state of the most topical problems in physics and in associated fields. The presented News is devoted to the fundamental discoveries of physics and astrophysics. Permanent editor is Yu.N. Eroshenko. It is compiled from a multitude of Internet sources. | |
|
© 1918–2024 Uspekhi Fizicheskikh Nauk Email: ufn@ufn.ru Editorial office contacts About the journal Terms and conditions |