Physics at its coolest

Tuoriniemi, Juha

doi:10.1038/nphys3616

Cited by 10 publications

(7 citation statements)

References 34 publications

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“…The extension of classical thermodynamics for modern physics (non-Gaussian Brownian diffusion in soft-matter [19], microscale engines, and motors [20][21][22]) out of equilibrium systems (granular gas and materials [23][24][25], the construction of phase diagrams in hard sphere packing in three dimension [26], and plasma [27]) and open systems is an active emerging field of research. The limit and breakdown of adiabaticity has been analytically and numerically studied in quantum systems [3]; subsequently, possible experimental testing using ultracold gases has been discussed [28,29]. Here, we have removed the effect of plasma boundaries and related electric field on a farfrom-equilibrium magnetically expanding electron gas, allowing it to interact solely with the magnetic wall, demonstrating an adiabatic expansion.…”

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confidence: 99%

Adiabatic Expansion of Electron Gas in a Magnetic Nozzle

et al. 2018

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A specially constructed experiment shows the near perfect adiabatic expansion of an ideal electron gas resulting in a polytropic index greater than 1.4, approaching the adiabatic value of 5/3, when removing electric fields from the system, while the polytropic index close to unity is observed when the electrons are trapped by the electric fields. The measurements were made on collisionless electrons in an argon plasma expanding in a magnetic nozzle. The collision lengths of all electron collision processes are greater than the scale length of the expansion, meaning the system cannot be in thermodynamic equilibrium, yet thermodynamic concepts can be used, with caution, in explaining the results. In particular, a Lorentz force, created by inhomogeneities in the radial plasma density, does work on the expanding magnetic field, reducing the internal energy of the electron gas that behaves as an adiabatically expanding ideal gas.

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confidence: 99%

Adiabatic Expansion of Electron Gas in a Magnetic Nozzle

et al. 2018

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“…These generic relations are based on the principle of entropy conservation in a thermodynamic system during adiabatic process. They constitute the basis for the nuclear spin cooling by adiabatic demagnetisation, a widely used cryogenic technique 4,[11][12][13] . The nuclear spin temperature may take either positive or negative values, in the latter case the magnetisation being anti-parallel to the applied field.…”

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confidence: 99%

“…Various optical and magnetic techniques have been employed to measure nuclear spin temperature, mostly by the magnetisation measurement at a fixed value of the external magnetic field 4,11,[14][15][16] . On the other hand, a direct measurement of the nuclear magnetisation as a function of slowly varying magnetic field is extremely challenging and has never been realised to the best of our knowledge.…”

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Spin temperature concept verified by optical magnetometry of nuclear spins

et al. 2018

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We develop a method of non-perturbative optical control over adiabatic remagnetisation of the nuclear spin system and apply it to verify the spin temperature concept in GaAs microcavities. The nuclear spin system is shown to exactly follow the predictions of the spin-temperature theory, despite the quadrupole interaction that was earlier reported to disrupt nuclear spin thermalisation. These findings open a way to deep cooling of nuclear spins in semiconductor structures, with a prospect of realisation of nuclear spin-ordered states for high fidelity spin-photon interfaces.The concept of nuclear spin temperature is one of the cornerstones of the nuclear magnetism in solids 1,2 . It has made possible realisation of the cryogenic cooling into the microKelvin range 3 and observation of nuclear spin ordering in metals and insulators 4,5 . Such degree of control of the nuclear spin system (NSS) in semiconductor heterostructures would allow enhancing the efficiency of spin-based information storage and processing 6-9 . However, proving the validity of the spin temperature concept for semiconductor nano-and microstructures is challenging due to the lack of techniques capable of precise sensing of weak nuclear magnetisation in a small volume. In addition, recent experiments showed that in quantum dots, where strong quadrupole-induced local fields have been reported, nuclear spin temperature failed to establish 10 . In this context, NSS thermalisation sensing in semiconductor heterostructures is one the central issues for both fundamental questions related to the realisation of nuclear spin-ordered states, and for potential applications, such as high fidelity spin-photon interfaces 6-9 .The basic postulates of the spin temperature theory are illustrated in Fig. 1(a). It is assumed that during the characteristic time T 2 determined by spin-spin interactions the NSS reaches the internal equilibrium. This means that properties of the NSS are governed by a single parameter, the spin temperature Θ N . When this temperature is made different from the lattice temperature Θ L (e.g. by the optical pumping), the thermalisation of the NSS with the crystal lattice usually requires a much longer characteristic time T 1 . Fig.1(b) illustrates one of the main predictions of the spin temperature theory: if the NSS is subjected to a slowly varying magnetic field, such that dB/dt < B L /T 2 , then Θ N and the nuclear spin polarisation P N change obeying universal expressions:(1) Here γ N is the gyromagnetic ratio of the nuclear spin I, angular brackets denote the averaging over all nuclear species, k B is the Boltzman constant, and Θ N i is the spin temperature at strong magnetic field B i >> B L , where B L is the local field induced by the fluctuating nuclear spins. These generic relations are based on the principle of entropy conservation in a thermodynamic system during adiabatic process. They constitute the basis for the nuclear spin cooling by adiabatic demagnetisation, a widely used cryogenic technique 4,11-13 . The nuclear spin tem...

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“…Cryogenics has developed as a branch of physics due to the efforts towards liquefying noble gases. It is fair to claim that the liquefaction of helium is the beginning of the physics of low temperatures [ 1 ]. Currently, cryogenics can be considered as a science located at the intersection of physics and engineering.…”

Section: Cryogenics Backgroundmentioning

confidence: 99%

Cryogenic Cooling in Wireless Communications

Markiewicz

Wesołowski

2019

Entropy

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Improving the capacity and performance of communication systems is typically achieved by either using more bandwidth or enhancing the effective signal-to-noise ratio (SNR). Both approaches have led to the invention of various transmission techniques, such as forward error correction (FEC), multiple-input multiple-output (MIMO), non-orthogonal multiple access (NOMA), and many, many others. This paper, however, focuses on the idea that should be immediately apparent when looking at Shannon’s channel capacity formula, but that somehow remained less explored for decades, despite its (unfortunately only in theory) limitless potential. We investigate the idea of improving the performance of communication systems by means of cryogenic cooling of their RF front-ends; the technique, although widely-known and used in radio astronomy for weak signal detection, has attracted limited interest when applied to wireless communications. The obtained results, though mainly theoretical, are promising and lead to a substantial channel capacity increase, implying an increase in spectral efficiency, potential range extension, or decreasing the power emitted by mobile stations. We see its applications in base stations (BSs) of machine-type communication (MTC) and Internet of Things (IoT) systems.

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Physics at its coolest

Cited by 10 publications

References 34 publications

Adiabatic Expansion of Electron Gas in a Magnetic Nozzle

Adiabatic Expansion of Electron Gas in a Magnetic Nozzle

Spin temperature concept verified by optical magnetometry of nuclear spins

Cryogenic Cooling in Wireless Communications

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