Continuous Faraday measurement of spin precession without light shifts

Abstract

We describe a dispersive Faraday optical probe of atomic spin which performs a weak measurement of spin projection of a quantum gas continuously for more than one second. To date focusing bright far-off-resonance probes onto quantum gases has proved invasive, due to strong scalar and vector light shifts exerting dipole and Stern-Gerlach forces. We show that tuning the probe near the magiczero wavelength at 790 nm between the fine-structure doublet of 87 Rb cancels the scalar light shift, and careful control of polarization eliminates the vector light shift. Faraday rotations due to each fine-structure line reinforce at this wavelength, enhancing the signal-to-noise ratio for a fixed rate of probe-induced decoherence. Using this minimally-invasive spin probe we perform microscale atomic magnetometry at high temporal resolution. Spectrogram analysis of the Larmor precession signal of a single spinor Bose-Einstein condensate measures a time-varying magnetic field strength with 1 µG accuracy every 5 ms; or equivalently makes > 200 successive measurements each at 10 pT/ √ Hz sensitivity.

Realization of a deeply subwavelength adiabatic optical lattice

“…Following the calculation of the scattering rate at the magic-zero wavelength in Refs. [43,44], we find that the scattering rate for a single beam with intensity I 0 is…”

“…Following the calculation of the scattering rate at the magic-zero wavelength in Refs. [ 43 , 44 ], we find that the scattering rate for a single beam with intensity I 0 is where Δ D 1 and Δ D 2 are the detuning of the laser from the D 1 and D 2 lines (the 5 S 1/2 to 5 P 1/2 or to 5 P 3/2 transitions, respectively). The polarizability constant , where λ D 2 and Γ D 2 are the resonant wavelength and natural linewidth of the D 2 transition.…”

Measurement of a Li7 tune-out wavelength by phase-patterned atom interferometry

“…TO wavelengths are important in fundamental and applied physics, offering a versatile tool in quantum state engineering [24]. Since TO wavelengths are unique to a specific state, they can be used to create species-and state-dependent potentials [25][26][27][28][29] and for minimizing measurement backaction [30]. Precision measurements of TO wavelengths [31][32][33][34][35][36][37][38] may also be used to test all-order atomic theory [24,39,40] and QED [41,42].…”

Error-disturbance uncertainty relations in Faraday measurements

“…Recently, the Faraday measurements of spin based on an atom-light interface framework have been studied actively [68][69][70][71][72][73][74][75][76][77][78]. It has contributed to our understating of quantum measurement and has various applications in quantum metrology of atomic ensemble [79], quantum information processing [80], strongly correlated systems [81], and many-body systems [82].…”