We describe an array of spin-exchange-relaxation-free optical magnetometers designed for detection of fetal magnetocardiography (fMCG). The individual magnetometers are configured with a small volume with intense optical pumping, surrounded by a large pump-free region. Spin-polarized atoms that diffuse out of the optical pumping region precess in the ambient magnetic field and are detected by a probe laser. Four such magnetometers, at the corners of a 7 cm square, are configured for gradiometry by feeding back the output of one magnetometer to a field coil to null uniform magnetic field noise at frequencies up to 200 Hz. We present the first measurements of fMCG signals using an atomic magnetometer.

We present a portable four-channel atomic magnetometer array operating in the spin exchange relaxation-free regime. The magnetometer array has several design features intended to maximize its suitability for biomagnetic measurement, specifically foetal magnetocardiography, such as a compact modular design and fibre coupled lasers. The modular design allows the independent positioning and orientation of each magnetometer. Using this array in a magnetically shielded room, we acquire adult magnetocadiograms. These measurements were taken with a 6–11 fT Hz−1/2 single-channel baseline sensitivity that is consistent with the independently measured noise level of the magnetically shielded room.

The competition of magnetic exchange interactions and tunneling underlies many complex quantum phenomena observed in real materials. We study non-equilibrium magnetization dynamics in an extended 2D system by loading effective spin-1/2 bosons into a spin-dependent optical lattice, and we use the lattice to separately control the resonance conditions for tunneling and superexchange. After preparing a non-equilibrium anti-ferromagnetically ordered state, we observe relaxation dynamics governed by two well-separated rates, which scale with the underlying Hamiltonian parameters associated with superexchange and tunneling. Remarkably, with tunneling off-resonantly suppressed, we are able to observe superexchange dominated dynamics over two orders of magnitude in magnetic coupling strength, despite the presence of vacancies. In this regime, the measured timescales are in agreement with simple theoretical estimates, but the detailed dynamics of this 2D, strongly correlated, and far-from-equilibrium quantum system remain out of reach of current computational techniques.The interplay of spin and motion underlies some of the most intriguing and poorly understood behaviors in many-body quantum systems [1]. A well known example is the onset of superconductivity in cuprate compounds when mobile holes are introduced into an otherwise insulating 2D quantum magnet [2]; understanding this behavior is particularly challenging because the dimensionality is low enough to support strong quantum correlations, but high enough to prohibit numerical solution. Ultracold atoms in optical lattices realize tunable, idealized models of such behavior, and can naturally operate in a regime where the quantum motion (tunneling) of particles and magnetic interactions (superexchange) explicitly compete [3,4].For ultracold atoms in equilibrium, the extremely small energy scale associated with superexchange interactions makes the observation of magnetism challenging, and short-range antiferromagnetic correlations resulting from superexchange have only recently been observed [5,6]. Out of equilibrium, superexchange-dominated dynamics has been demonstrated in isolated pairs of atoms [7], in 1D systems with single atom spin impurities [8], and recently in the decay of spin-density waves [9]. However, the perturbative origin of superexchange in these systems requires that it be weak compared to tunneling, and thus the manifestation of superexchange requires extremely low motional entropy. Dipolar gases [10] and ultracold polar molecules [11] in lattices provide a promising route toward achieving large (non-perturbative) magnetic interactions [12], but, technical limitations in these systems currently complicate the simultaneous observation of motional and spin-exchange effects.Here, we study the magnetization dynamics of effective spin-1/2 bosons in a 2D optical lattice following a global quench from an initially antiferromagnetically ordered state [13]. The dynamics we observe is governed by a bosonic t-J model [14,15]. Utilizing a checkerboard optical...

We present measurements, by using two complementary methods, of the breakdown of atomic angular momentum selection rules in He-broadened Rb vapor. Atomic dark states are rendered weakly absorbing due to fine-structure mixing during Rb-He collisions. The effect substantially increases the photon demand for optical pumping of dense vapors.