Characterization of noise sources in a microfabricated single-beam zero-field optically-pumped magnetometer.

We present an experimental noise characterization of a miniature single-beam absorption-based optically-pumped magnetometer with a noise floor of 7 fT/Hz1/2 operating in the spin-exchange relaxation-free regime. We experimentally evaluate noise arising from the laser intensity, laser frequency, laser polarization, cell temperature, and magnetic field coils used for the phase-sensitive detection of the magnetometer signal. We find that noise in the range between DC and 30 Hz is a result of noise sources coupling to the atoms in a manner similar to a magnetic field, while the noise at frequencies above 30 Hz is mainly due to laser intensity noise. Our results place an upper limit on the noise sources for our system that matches well with the noise spectrum of the magnetometer at frequencies above 5 Hz.

Prospects for magnetic field communications and location using quantum sensors.

Signal attenuation limits the operating range in wireless communications and location. To solve the reduced range problem, we can use low-frequency signals in combination with magnetic sensing. We propose the use of an optically pumped magnetometer as a sensor and realize a proof-of-principle detection of binary phase shift keying (BPSK) modulated signals. We demonstrate a ranging enhancement by exploiting both the magnetometer's intrinsic sensitivity of below 1 pT/Hz1/2 and its 1 kHz operating bandwidth through the use of BPSK signals.

Improved limit on a temporal variation of mp/me from comparisons of Yb+ and Cs atomic clocks.

Accurate measurements of different transition frequencies between atomic levels of the electronic and hyperfine structure over time are used to investigate temporal variations of the fine structure constant α and the proton-to-electron mass ratio µ. We measure the frequency of the (2)S1/2→(2)F7/2 electric octupole (E3) transition in (171)Yb(+) against two caesium fountain clocks as f(E3)=642,121,496,772,645.36 Hz with an improved fractional uncertainty of 3.9×10(-16). This transition frequency shows a strong sensitivity to changes of α. Together with a number of previous and recent measurements of the (2)S1/2→(2)D3/2 electric quadrupole transition in (171)Yb(+) and with data from other elements, a least-squares analysis yields (1/α)(dα/dt)=-0.20(20)×10(-16)/yr and (1/µ)(dµ/dt)=-0.5(1.6)×10(-16)/yr, confirming a previous limit on dα/dt and providing the most stringent limit on dµ/dt from laboratory experiments.

Compact phase delay technique for increasing the amplitude of coherent population trapping resonances in open Lambda systems.

We propose and demonstrate a novel technique for increasing the amplitude of coherent population trapping (CPT) resonances in open Lambda systems. The technique requires no complex modifications to the conventional CPT setup and is compatible with standard microfabrication processes. The improvement in the CPT resonance amplitude as a function of intensity of the excitation light agrees well with the theory based on ideal open and closed Lambda systems.

Atomic-based stabilization for laser-pumped atomic clocks.

We describe a novel technique for stabilizing frequency shifts in laser-interrogated vapor-cell atomic clocks. The method suppresses frequency shifts due to changes in the laser frequency, intensity, and modulation index as well as atomic vapor density. The clock operating parameters are monitored by using the atoms themselves, rather than by using conventional schemes for laser frequency and cell temperature control. The experiment is realized using a chip-scale atomic clock. The novel atomic-based stabilization approach results in a simpler setup and improved long-term performance.

Atomic vapor cells for chip-scale atomic clocks with improved long-term frequency stability.

A novel technique for microfabricating alkali atom vapor cells is described in which alkali atoms are evaporated into a micromachined cell cavity through a glass nozzle. A cell of interior volume 1 mm3, containing 87Rb and a buffer gas, was made in this way and integrated into an atomic clock based on coherent population trapping. A fractional frequency instability of 6 x 10(-12) at 1000 s of integration was measured. The long-term drift of the F=1, mF=0-->F=2, mF=0 hyperfine frequency of atoms in these cells is below 5 x 10(-11)/day.

High-resolution spectroscopy with a femtosecond laser frequency comb.

The output of a mode-locked femtosecond laser is used for precision single-photon spectroscopy of 133Cs in an atomic beam. By changing the laser's repetition rate, the cesium D1 (6s 2S(1/2)-->6p 2P(1/2)) and D2 (6s 2S(1/2)-->6p 2P(3/2)) transitions are detected and the optical frequencies are measured with accuracy similar to that obtained with a cw laser. Control of the femtosecond laser repetition rate by use of the atomic fluorescence is also implemented, thus realizing a simple cesium optical clock.