The invention relates to a method which makes use of the Zeeman effect for measuring magnetic fields, by way of dark resonances. According to said method, a measuring cell (14) is exposed to the magnetic field (B) to be measured and contains the atoms of a measuring medium in a buffer gas, a radiation source (11) being provided for exciting the atoms by radiation and being connected to the modulation frequency generator and emitting electromagnetic radiation with different frequencies. A frequency detector (17) is mounted downstream of the measuring cell (14) and comprises a control loop (18) for the frequency tuning to a dark resonance frequency. The invention is characterized in that at least one modulator (22) for modulating a comparatively high first modulation frequency with a lower second modulation frequency, thereby producing a double sideband structure, is mounted downstream of the modulation frequency generator (24) to couple a plurality of dark resonances using the electromagnetic radiation (12) modulated therewith, substantially only one frequency being detected according to the magnetic field-dependent frequency shift.

Method and device for measuring magnetic fields

Mode stability is an important performance characteristic of external cavity diode lasers (ECDLs). It has been well established that the continuous mode-hop-free tuning range of a grating-feedback ECDL can be optimized by rotating the grating about a specific pivot location. We show that similar results can be obtained for other more convenient pivot locations by choosing instead the cavity length and grating location. The relative importance of the temperature stability of the diode and of the external cavity is also evaluated. We show that mechanically simple ECDL designs, using mostly standard components, can readily achieve a 35 GHz mode-hop-free tuning range at 780 nm.

Mode stability of external cavity diode lasers

Rare-earth ions doped in solid-state materials are considered promising candidates for quantum information applications, especially for photonic quantum memory. Among them, erbium ions doped in an optical fiber have attracted a lot of attentions due to their ability to provide efficient photon-atom interaction on a telecom-C band compatible transition. The coherent photon-atom interaction, which is crucial for quantum memory, has not yet been investigated for erbium ions doped in fiber at the temperature of sub 10 mKlinebreak with the magnetic environment. In this paper, we experimentally observe optical nutation, which results from the coherent interaction between laser and erbium ions ensemble, in a piece of 9.5-m-long fiber with the erbium concentration of 200 ppm. We also extract the transition dipole moment from the results of optical nutation and further investigate its dependence on laser wavelength and magnetic field. A transition dipole moment of (3.424$\\pm$0.019)$\\times$10$^{-32}$ C$\\cdot$m is obtained at the wavelength of 1537 nm and magnetic field of 0.2 T. Our results could pave the way for realizing solid-state quantum networks at telecom-C band.

Experimental observation of coherent interaction between laser and erbium ions ensemble doped in fiber at sub 10 mK

Two-color polarization spectroscopy of rubidium

The invention provides spectroscopy apparatuses and methods allowing precise overlapping between circularly polarized pump beam and a counter propagating linearly polarized probe beams in a sample which presents unique advantages for precision spectroscopy. In general, the apparatus comprises a phase retarding element with which by double pass by retro reflection of an incident beam turn linearly polarized light to circular and vice versa. This unique configuration enable to design a compact and miniature apparatus which may be applied for measuring polarization spectroscopy, nonlinear optical rotation and coherent population trapping phenomena with certain advantages resulting from the unique optical arrangement. The design of the apparatus further facilitates integration and scaling to produce arrays of units which may be particularly useful for magnetometry applications. Other important applications of the invention include laser frequency stabilization and atomic clocks.

A method and apparatus for high precision spectroscopy

We present experimental results demonstrating enhanced current modulation of an antireflection-coated edge-emitting laser diode placed in an external cavity. By eliminating the internal cavity of the laser diode and matching the external cavity free spectral range to the modulation frequency we have increased the modulation response up to nearly complete carrier suppression. We demonstrate the tunability of this enhanced modulation over a range of more than 3 GHz. The power of the modulated beam has been measured to be 10 mW. We have recorded a beat note between the first two optical sidebands of width 1 Hz at 6.834 GHz (corresponding to the hyperfine splitting of the 87Rb ground state). This technique enables the generation of two high-power phase-locked beams for coherent manipulation of atomic states.

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Modulation enhancement of a laser diode in an external cavity

We describe and characterize alternative configurations for Doppler-free polarization spectroscopy. The suggested apparatus enables complete pump/probe beam overlap and allows substantial miniaturization. Its utility and performance for narrow linewidth, high-stability frequency locking is discussed for the |5S1/2F=2⟩→|5P3/2F′⟩D2 transition in R87b.

Retroreflecting polarization spectroscopy enabling miniaturization

A device and a method enabling the enhancing of the modulation efficiency of lasers by matching the modulation frequency and the FSR of the laser. This is optionally achieved by eliminating the internal cavity of a laser diode (103) placed in an external cavity and matching the FSR of the external cavity to the modulation frequency. The modulation index is enhanced to and beyond the point of complete carrier suppression even at high modulation frequency and high beam intensities. The external cavity comprises a grating (107), the cavity length being adjusted with a PZT (108) and a translation stage (109). The laser diode (103) is driven by a bias current (110) from a driver (115) and a modulation current (111) from a modulation driver (116).

Phase locked sideband beams by bias modulation of an external cavity laser diode having a grating

In this invited review in honor of 100 years since the Stern-Gerlach (SG) experiments, we describe a decade of SG interferometry on the atom chip. The SG effect has been a paradigm of quantum mechanics throughout the last century, but there has been surprisingly little evidence that the original scheme, with freely propagating atoms exposed to gradients from macroscopic magnets, is a fully coherent quantum process. Specifically, no full-loop SG interferometer (SGI) has been realized with the scheme as envisioned decades ago. Furthermore, several theoretical studies have explained why it is a formidable challenge. Here we provide a review of our SG experiments over the last decade. We describe several novel configurations such as that giving rise to the first SG spatial interference fringes, and the first full-loop SGI realization. These devices are based on highly accurate magnetic fields, originating from an atom chip, that ensure coherent operation within strict constraints described by previous theoretical analyses. Achieving this high level of control over magnetic gradients is expected to facilitate technological applications such as probing of surfaces and currents, as well as metrology. Fundamental applications include the probing of the foundations of quantum theory, gravity, and the interface of quantum mechanics and gravity. We end with an outlook describing possible future experiments.

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Stern-Gerlach Interferometry with the Atom Chip

We analyze theoretically and experimentally the existence of a magic frequency for which the absorption of a linearly polarized light beam by a vapor of alkali-metal atoms is independent of the population distribution among the Zeeman sublevels and the angle between the beam and a magnetic field. The phenomenon originates from a peculiar cancellation of the contributions of higher moments of the atomic density matrix, and is described using the Wigner-Eckart theorem and inherent properties of Clebsch-Gordan coefficients. One important application is the robust measurement of the hyperfine population.

Menachem Givon

Papers

Modulation enhancement of a laser diode in an external cavity

Retroreflecting polarization spectroscopy enabling miniaturization

Phase locked sideband beams by bias modulation of an external cavity laser diode having a grating

Stern-Gerlach Interferometry with the Atom Chip

Magic frequencies in atom-light interaction for precision probing of the density matrix.