Bose-Einstein condensation (BEC) has been observed in a dilute gas of sodium atoms. A Bose-Einstein condensate consists of a macroscopic population of the ground state of the system, and is a coherent state of matter. In an ideal gas, this phase transition is purely quantum-statistical. The study of BEC in weakly interacting systems which can be controlled and observed with precision holds the promise of revealing new macroscopic quantum phenomena that can be understood from first principles.

Bose-Einstein condensation in a gas of sodium atoms

Fiber ring interferometer

radar echo delay, black holes and gravitational waves. It is worth pointing out that even here the author goes beyond a mere introduction, for example in the analysis of the phase diagram of cosmological parameters, the calculation of the first acoustic peak in the spectrum of the cosmic microwave background, the discussion of the precession of gyroscopes, the utilisation of Penrose diagrams to understand the causal structure of spacetime and the study of rotating black holes. Gravitational lensing, despite its important role in modern astronomy, is not covered at all. After just under 600 pages, the reader is already well versed in general relativity and many of its most important applications. Where many other textbook authors would have stopped, Zee goes on and continues with more advanced and modern subjects that will prepare the student to start doing research in the area. Maximally symmetric spaces, the vielbein formalism, conformal algebra, de Sitter and anti de Sitter spacetime, Kaluza– Klein theory, brane worlds, topological field theory and twistors are some of the more exotic topics the author addresses. These chapters make Zee’s book incredibly worthwhile, since treatments at the undergraduate level of these subjects hardly exist. All in all, Zee succeeded to write a unique textbook on general relativity. His narrative is exciting and well structured, but he also does not shy away from computations when they are necessary. The logical steps in attacking a problem are always presented very transparently, making it easier for the novice to become familiar with the material. The book is beautifully typeset and richly illustrated. It contains exercises at the end of each chapter and solutions to selected exercises in the appendix, together with a detailed index and a collection of important formulae. I strongly recommend this book to anyone interested in understanding general relativity.

Optical Magnetometry: Scope: reference. Level: postgraduate

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Laser Spectroscopy Basic Concepts And Instrumentation

Optically pumped magnetometers: From quantum origins to multi-channel magnetoencephalography.

This paper aims to review the technology, developments, and applications of spin exchange relaxation free (SERF) atomic magnetometers. The generalized comparisons between the SERF magnetometer and the other types of weak magnetic sensors are elaborated. Further, the fundamental composition and operational principle of the SERF atomic magnetometer are elucidated. The development history and recent technological developments with respect to several aspects, including the alkali metal vapor source, atom heating method, pump and probe lasers, and magnetic shielding system, are presented. The classification and respective advantages and disadvantages of these technologies are described in detail. Finally, the existing and potential applications, as well as the prospective future development trends are presented.

SERF Atomic Magnetometer–Recent Advances and Applications: A Review

A precision measurement of the Earth's rotation is reported by using a K-Rb-${}^{21}$Ne comagnetometer, where it is found that the existence of the light shift arising from the circularly polarized pump laser enables the comagnetometer to sense dual-axis rotations.

Rotation sensing using a K-Rb- Ne 21 comagnetometer

We describe a dual-axis atomic spin gyroscope based on an alkali metal-noble gas comagnetometer. Alkali metal vapor is optically pumped, and then the noble gas is hyperpolarized along the z axis. When sensing a transverse rotation, the polarized noble gas will be induced to precess and produce an effective magnetic field in the x – y plane for alkali metals to precess under. Operating in the spin-exchange relaxation-free regime, alkali atoms are modulated by the z axis magnetic field and serve as an integrated in-situ dual-axis magnetometer to detect the gyroscopic precession in the x and y axes simultaneously, using a single probe beam. By using the parametric modulation technique, the low frequency drift is effectively suppressed and a bias instability of less than 0.05 deg/h has been achieved in our dual-axis atomic spin gyroscope.

A parametrically modulated dual-axis atomic spin gyroscope

In a hybrid pumping alkali-metal vapor cell filled with both K and Rb atoms, the K atom spins are optically pumped by the laser and the Rb atom spins are polarized by the K spins through spin exchange. We discovered that the ac Stark shift of the Rb atom spins, caused by the far-off-resonant pumping laser tuned to the K absorption lines, was mixed together with the ac Stark shift of the K atom spins through fast spin exchange. This mixing is studied and we demonstrate a K-Rb-$^{21}\mathrm{Ne}$ comagnetometer in which the ac Stark shift of the Rb atom spins is eliminated by compensating for the Rb ac Stark shift with the K ac Stark shift. An ac Stark shift elimination method has been developed.

Spin-exchange collision mixing of the K and Rb ac Stark shifts

A novel method to compensate the residual magnetic field for an atomic magnetometer consisting of two perpendicular beams of polarizations was demonstrated in this paper. The method can realize magnetic compensation in the case where the pumping rate of the probe beam cannot be ignored. In the experiment, the probe beam is always linearly polarized, whereas, the probe beam contains a residual circular component due to the imperfection of the polarizer, which leads to the pumping effect of the probe beam. A simulation of the probe beam's optical rotation and pumping rate was demonstrated. At the optimized points, the wavelength of the probe beam was optimized to achieve the largest optical rotation. Although, there is a small circular component in the linearly polarized probe beam, the pumping rate of the probe beam was non-negligible at the optimized wavelength which if ignored would lead to inaccuracies in the magnetic field compensation. Therefore, the dynamic equation of spin evolution was solved by considering the pumping effect of the probe beam. Based on the quasi-static solution, a novel magnetic compensation method was proposed, which contains two main steps: (1) the non-pumping compensation and (2) the sequence compensation with a very specific sequence. After these two main steps, a three-axis in situ magnetic compensation was achieved. The compensation method was suitable to design closed-loop spin-exchange relaxation-free magnetometer. By a combination of the magnetic compensation and the optimization, the magnetic field sensitivity was approximately 4 fT/Hz1/2, which was mainly dominated by the noise of the magnetic shield.

Wei Quan

Papers

SERF Atomic Magnetometer–Recent Advances and Applications: A Review

Rotation sensing using a K-Rb- Ne 21 comagnetometer

A parametrically modulated dual-axis atomic spin gyroscope

Spin-exchange collision mixing of the K and Rb ac Stark shifts

In situ magnetic compensation for potassium spin-exchange relaxation-free magnetometer considering probe beam pumping effect.