Using the Earth as a polarized electron source to search for long-range spin-spin interactions

New Classes of Magnetic Noise Self-Compensation Effects in Atomic Comagnetometer

Precision measurements of anomalous spin-dependent interactions are often hindered by magnetic noise and other magnetic systematic effects. Atomic comagnetometers use the distinct spin precession of two species and have emerged as important tools for effectively mitigating the magnetic noise. Nevertheless, the operation of existing comagnetometers is limited to very low-frequency noise commonly below 1 Hz. Here, we report a new type of atomic comagnetometer based on a magnetic noise self-compensation mechanism originating from the destructive interference between alkali-metal and noble-gas spins. Our comagnetometer employing K-^{3}He system remarkably suppresses magnetic noise exceeding 2 orders of magnitude at higher frequencies up to 160 Hz. Moreover, we discover that the capability of our comagnetometer to suppress magnetic noise is spatially dependent on the orientation of the noise and can be conveniently controlled by adjusting the applied bias magnetic field. Our findings open up new possibilities for precision measurements, including enhancing the search sensitivity of spin-dark matter particles interactions into unexplored parameter space.

New Constraints on Exotic Spin-Spin-Velocity-Dependent Interactions with Solid-State Quantum Sensors

We report new experimental results on exotic spin-spin-velocity-dependent interactions between electron spins. We designed an elaborate setup that is equipped with two nitrogen-vacancy (NV) ensembles in diamonds. One of the NV ensembles serves as the spin source, while the other functions as the spin sensor. By coherently manipulating the quantum states of two NV ensembles and their relative velocity at the micrometer scale, we are able to scrutinize exotic spin-spin-velocity-dependent interactions at short force ranges. For a T-violating interaction, V_{6}, new limits on the corresponding coupling coefficient, f_{6}, have been established for the force range shorter than 1 cm. For a P,T-violating interaction, V_{14}, new constraints on the corresponding coupling coefficient, f_{14}, have been obtained for the force range shorter than 1 km.

Search for Spin-Dependent Gravitational Interactions at Earth Range

Among the four fundamental forces, only gravity does not couple to particle spins according to the general theory of relativity. We test this principle by searching for an anomalous scalar coupling between the neutron spin and the Earth's gravity on the ground. We develop an atomic gas comagnetometer to measure the ratio of nuclear spin-precession frequencies between ^{129}Xe and ^{131}Xe, and search for a change of this ratio to the precision of 10^{-9} as the sensor is flipped in Earth's gravitational field. The null results of this search set an upper limit on the coupling energy between the neutron spin and the gravity on the ground at 5.3×10^{-22}  eV (95% confidence level), resulting in a 17-fold improvement over the previous limit. The results can also be used to constrain several other anomalous interactions. In particular, the limit on the coupling strength of axion-mediated monopole-dipole interactions at the range of Earth's radius is improved by a factor of 17.

Search for exotic parity-violation interactions with quantum spin amplifiers

Quantum sensing provides sensitive tabletop tools to search for exotic spin-dependent interactions beyond the standard model, which have attracted great attention in theories and experiments. Here, we develop a technique based on Spin Amplifier for Particle PHysIcs REsearch (SAPPHIRE) to resonantly search for exotic interactions, specifically parity-odd spin-spin interactions. The present technique effectively amplifies exotic interaction fields by a factor of about 200 while being insensitive to spurious magnetic fields. Our studies, using such a quantum amplification technique, explore the parity-violation interactions mediated by a new vector boson in the challenging parameter space (force range between 3 mm and 1 km) and set the most stringent constraints on axial-vector electron-neutron couplings, substantially improving previous limits by five orders of magnitude. Moreover, our constraints on axial-vector couplings between nucleons reach into a hitherto unexplored parameter space. The present constraints complement the existing astrophysical and laboratory studies on potential standard model extensions.

Environment-dependent fluctuations of potentiometric pH dynamics in geomagnetic field

This work explores fluctuations of potentiometric pH dynamics in environments with different configurations of geomagnetic fields. High-resolution pH measurements of test liquids are conducted in electromagnetically shielded and thermally stabilized conditions. External measurement environment in two laboratories is modulated by non-conducting/non-magnetic objects of organic and inorganic origins. Totally, 88 experiments in three groups have been conducted during 4 months. The affected pH dynamics at the level of 10^-2-10^-5 pH is detected in 93.5%, 82.2% and 74.4% depending on dielectric permittivity of environmental objects. Reaction of potentiometric system has a typical delay of 30-180 minutes. Experiments in both laboratories demonstrated 19% difference of reproducibility rate caused by different background fluctuations. To explain the obtained results, the paper discusses the effects of the Earth's electric and magnetic fields in the form of magnetospheric Poynting vectors or spin-spin forces in geomagnetic field, which affects the productivity of ionic and free-radical reactions. Since the pH level of aqueous solutions controls various biochemical reactions, this mechanism can explain several biological effects with non-contact signal transmission observed in environmental biology and electromagnetic biophysics.

Limits on Axions and Axionlike Particles within the Axion Window Using a Spin-Based Amplifier

Searches for the axion and axionlike particles may hold the key to unlocking some of the deepest puzzles about our Universe, such as dark matter and dark energy. Here, we use the recently demonstrated spin-based amplifier to constrain such hypothetical particles within the well-motivated "axion window" (10  μeV-1  meV) through searching for an exotic dipole-dipole interaction between polarized electron and neutron spins. The key ingredient is the use of hyperpolarized long-lived ^{129}Xe nuclear spins as an amplifier for the pseudomagnetic field generated by the exotic interaction. Using such a spin sensor, we obtain a direct upper bound on the product of coupling constants g_{p}^{e}g_{p}^{n}. The spin-based amplifier technique can be extended to searches for a wide variety of hypothetical particles beyond the standard model.

Transverse light-shift in a spin-exchange relaxation-free co-magnetometer: measurement, decoupling, and suppression

The transverse light-shift can induce non-negligible polarization error in the output signal of spin-exchange relaxation-free (SERF) co-magnetometer. In this paper, a novel method for rapid measurement of transverse light-shift based on the error of steady-state response of co-magnetometer is proposed firstly, then the sources of transverse light-shift in a compact SERF co-magnetometer is modeled and analyzed from three aspects: the non-ideal linear polarization of probe laser, the circular dichroism of the atomic spin ensembles, and the stress-induced birefringence effect of the cell wall. Furthermore, the decoupling and suppression methods of transverse light-shift based on a degree of circular polarization (DOCP) regulation scheme is presented, to realize the decoupling measurement of the transverse light-shift introduced by the whole co-magnetometer cell, and cancel it out with the non-ideal linear polarization of the probe laser. Eventually, the DOCP regulation scheme suggested in this paper achieves more than a 67% suppression ratio in transverse light-shift, and the short- and long-term performance of SERF co-magnetometer are improved due to the reduction of the coupling effect between the probe laser power and transverse field. Moreover, the measurement, decoupling and suppression methods provided in this paper also have the potential to be applied to other atomic sensors, such as the SERF magnetometers and nuclear spin co-magnetometers.

Quantum Hydrodynamics of Spinning Particles in Electromagnetic and Torsion Fields

We develop a many-particle quantum-hydrodynamical model of fermion matter interacting with the external classical electromagnetic and gravitational/inertial and torsion fields. The consistent hydrodynamical formulation is constructed for the many-particle quantum system of Dirac fermions on the basis of the nonrelativistic Pauli-like equation obtained via the Foldy–Wouthuysen transformation. With the help of the Madelung decomposition approach, the explicit relations between the microscopic and macroscopic fluid variables are derived. The closed system of equations of quantum hydrodynamics encompasses the continuity equation, and the dynamical equations of the momentum balance and the spin density evolution. The possible experimental manifestations of the torsion in the dynamics of spin waves is discussed.

Search for exotic spin-dependent interactions with a spin-based amplifier

Development of new techniques to search for particles beyond the standard model is crucial for understanding the ultraviolet completion of particle physics. Several hypothetical particles are predicted to mediate exotic spin-dependent interactions between standard-model particles that may be accessible to laboratory experiments. However, laboratory searches are mostly conducted for static spin-dependent interactions, with a few experiments addressing spin- and velocity-dependent interactions. Here, we demonstrate a search for these interactions with a spin-based amplifier. Our technique uses hyperpolarized nuclear spins as an amplifier for pseudo-magnetic fields produced by exotic interactions by a factor of more than 100. Using this technique, we establish constraints on the spin- and velocity-dependent interactions between polarized neutrons and unpolarized nucleons for the force range of 0.03 to 100 meters, improving previous constraints by at least two orders of magnitude in partial force range. This technique can be further extended to investigate other exotic spin-dependent interactions.

Optimized Design of a Pump Laser System for a Spin Exchange Relaxation Free Inertial Measurement Device

In order to improve the precision and beam quality of a pump laser for a spin exchange relaxation free inertial measurement device, we applied one scheme to achieve the square wave modulation and power stability control of the pump laser and another one to obtain the uniform intensity distribution of the laser beam, in which the acousto-optic modulator (AOM) and proportion integration differentiation (PID) controller were used to achieve the former, and the freeform surface lens was designed and optimized to achieve the latter based on the TracePro software. In experiments, the first-order diffraction light beam coming through the AOM had a spot size of about 1.1×0.7 mm², and a spherical vapor cell with a radius of 7 mm was placed behind the freeform surface lens. Results show that the uniformity of the reshaped intensity distribution is higher than 90% within the target area with a radius of 7 mm both in the simulation and the experiment, which ensure that the uniform laser beam covers the area of cell. On the other hand, the power stability of the pump laser is controlled to be less than 0.05%. Compared with traditional methods, the complicated calculation process in optical design is better solved, and a higher uniformity with slight energy loss is achieved.

New Limits on Anomalous Spin-Spin Interactions

We report the results of a new search for long-range spin-dependent interactions using a Rb-^{21}Ne atomic comagnetometer and a rotatable electron spin source based on a SmCo_{5} magnet with an iron flux return. By looking for signal correlations with the orientation of the spin source we set new constraints on the product of the pseudoscalar electron and neutron couplings g_{p}^{e}g_{p}^{n}/ℏc<1.7×10^{-14} and on the product of their axial couplings g_{A}^{e}g_{A}^{n}/ℏc<5×10^{-42} to a new particle with a mass of less than about 1  μeV. Our measurements improve by about 2 orders of magnitude previous constraints on such spin-dependent interactions.

Bose-Einstein Condensate Comagnetometer

We describe a comagnetometer employing the f=1 and f=2 ground state hyperfine manifolds of a ^{87}Rb spinor Bose-Einstein condensate as colocated magnetometers. The hyperfine manifolds feature nearly opposite gyromagnetic ratios and thus the sum of their precession angles is only weakly coupled to external magnetic fields, while being highly sensitive to any effect that rotates both manifolds in the same way. The f=1 and f=2 transverse magnetizations and azimuth angles are independently measured by nondestructive Faraday rotation probing, and we demonstrate a 44.0(8) dB common-mode rejection in good agreement with theory. We show how the magnetometer coherence time can be extended to ∼1  s, by using spin-dependent interactions to inhibit hyperfine relaxing collisions between f=2 atoms. The technique could be used in high sensitivity searches for new physics on submillimeter length scales, precision studies of ultracold collision physics, and angle-resolved studies of quantum spin dynamics.

Miniaturized optical rotation detection system based on liquid crystal variable retarder in a K-Rb-21Ne gyroscope

A novel method to control the light intensity stability and modulate the probe light polarization using a liquid crystal variable retarder (LCVR) to detect atomic spin precession simultaneously in a K-Rb-²¹Ne gyroscope is reported. A sinusoidal driving voltage is applied to drive the LCVR and is skillfully used to produce a high-frequency modulation for the probe light. The modulation helps to avoid electronic detection noise appearing at low frequencies and allows for phase-sensitive detection. The coefficient of rate ramp can be reduced from 1.31 (deg/h)/h to 0.05 (deg/h)/h (Allan deviation), and the bias instability of about 0.08 deg/h at the averaging time of 200 s is achieved. Therefore, the long-term stability of the angular velocity measurement can be improved and other optical modulators can be replaced to facilitate the miniaturization of the gyroscope by using this intensity modulation detection method. This optical rotation detection method also can be applied to other miniaturized atomic sensors, such as atomic magnetometers.

Constraints on a Spin-Dependent Exotic Interaction between Electrons with Single Electron Spin Quantum Sensors

A new laboratory bound on the axial-vector mediated interaction between electron spins at micrometer scale is established with single nitrogen-vacancy (NV) centers in diamond. A single crystal of p-terphenyl doped pentacene-d_{14} under laser pumping provides the source of polarized electron spins. Based on the measurement of polarization signal via nitrogen-vacancy centers, we set a constraint for the exotic electron-electron coupling g_{A}^{e}g_{A}^{e}, within the force range from 10 to 900  μm. The obtained upper bound of the coupling at 500  μm is |g_{A}^{e}g_{A}^{e}/4πℏc|≤1.8×10^{-19}, which is one order of magnitude more stringent than a previous experiment. Our result shows that the NV center can be a promising platform for searching for new particles predicted by theories beyond the standard model.

Nuclear-Spin Comagnetometer Based on a Liquid of Identical Molecules

Atomic comagnetometers are used in searches for anomalous spin-dependent interactions. Magnetic field gradients are one of the major sources of systematic errors in such experiments. Here we describe a comagnetometer based on the nuclear spins within an ensemble of identical molecules. The dependence of the measured spin-precession frequency ratio on the first-order magnetic field gradient is suppressed by over an order of magnitude compared to a comagnetometer based on overlapping ensembles of different molecules. Our single-species comagnetometer is capable of measuring the hypothetical spin-dependent gravitational energy of nuclei at the 10^{-17}  eV level, comparable to the most stringent existing constraints. Combined with techniques for enhancing the signal such as parahydrogen-induced polarization, this method of comagnetometry offers the potential to improve constraints on spin-gravity coupling of nucleons by several orders of magnitude.

^{3}He-^{129}Xe Comagnetometery using ^{87}Rb Detection and Decoupling

We describe a ^{3}He-^{129}Xe comagnetometer using ^{87}Rb atoms for noble-gas spin polarization and detection. We use a train of ^{87}Rb π pulses and σ^{+}/σ^{-} optical pumping to realize a finite-field Rb magnetometer with suppression of spin-exchange relaxation. We suppress frequency shifts from polarized Rb by measuring the ^{3}He and ^{129}Xe spin precession frequencies in the dark, while applying π pulses along two directions to depolarize Rb atoms. The plane of the π pulses is rotated to suppress the Bloch-Siegert shifts for the nuclear spins. We measure the ratio of ^{3}He to ^{129}Xe spin precession frequencies with sufficient absolute accuracy to resolve Earth's rotation without changing the orientation of the comagnetometer. A frequency resolution of 7 nHz is achieved after integration for 8 h without evidence of significant drift.

Nuclear Matrix Elements for Tests of Local Lorentz Invariance Violation

The nuclear matrix elements for the spin operator and the momentum quadrupole operator are important for the interpretation of precision atomic physics experiments that search for violations of local Lorentz and CPT symmetry and for new spin-dependent forces. We use the configuration-interaction nuclear shell model and self-consistent mean-field theory to calculate the momentum matrix elements for ^{21}Ne, ^{23}Na, ^{133}Cs, ^{173}Yb, and ^{201}Hg. We show that these momentum matrix are strongly suppressed by the many-body correlations, in contrast to the well-known enhancement of the spatial quadrupole nuclear matrix elements.

Precessing Ferromagnetic Needle Magnetometer

A ferromagnetic needle is predicted to precess about the magnetic field axis at a Larmor frequency Ω under conditions where its intrinsic spin dominates over its rotational angular momentum, Nℏ≫IΩ (I is the moment of inertia of the needle about the precession axis and N is the number of polarized spins in the needle). In this regime the needle behaves as a gyroscope with spin Nℏ maintained along the easy axis of the needle by the crystalline and shape anisotropy. A precessing ferromagnetic needle is a correlated system of N spins which can be used to measure magnetic fields for long times. In principle, by taking advantage of rapid averaging of quantum uncertainty, the sensitivity of a precessing needle magnetometer can far surpass that of magnetometers based on spin precession of atoms in the gas phase. Under conditions where noise from coupling to the environment is subdominant, the scaling with measurement time t of the quantum- and detection-limited magnetometric sensitivity is t^{-3/2}. The phenomenon of ferromagnetic needle precession may be of particular interest for precision measurements testing fundamental physics.

Searching for New Spin- and Velocity-Dependent Interactions by Spin Relaxation of Polarized ^{3}He Gas

We have constrained possible new interactions which produce nonrelativistic potentials between polarized neutrons and unpolarized matter proportional to ασ[over →]·v[over →] where σ[over →] is the neutron spin and v[over →] is the relative velocity. We use existing data from laboratory measurements on the very long T_{1} and T_{2} spin relaxation times of polarized ^{3}He gas in glass cells. Using the best available measured T_{2} of polarized ^{3}He gas atoms as the polarized source and the Earth as an unpolarized source, we obtain constraints on two new interactions. We present a new experimental upper bound on possible vector-axial-vector (V_{VA}) type interactions for ranges between 1 and 10^{8} m. In combination with previous results, we set the most stringent experiment limits on g_{V}g_{A} ranging from ~μm to ~10^{8} m. We also report what is to our knowledge the first experimental upper limit on the possible torsion fields induced by the Earth on its surface. Dedicated experiments could further improve these bounds by a factor of ~100. Our method of analysis also makes it possible to probe many velocity dependent interactions which depend on the spins of both neutrons and other particles which have never been searched for before experimentally.

Constraints on Exotic Dipole-Dipole Couplings between Electrons at the Micrometer Scale

New constraints on exotic dipole-dipole interactions between electrons at the micrometer scale are established, based on a recent measurement of the magnetic interaction between two trapped 88Sr(+) ions. For light bosons (mass≤0.1  eV) we obtain a 90% confidence interval for an axial-vector-mediated interaction strength of |g(A)(e)g(A)(e)/4πℏc|≤1.2×10(-17). Assuming CPT invariance, this constraint is compared to that on anomalous electron-positron interactions, derived from positronium hyperfine spectroscopy. We find that the electron-electron constraint is 6 orders of magnitude more stringent than the electron-positron counterpart. Bounds on pseudoscalar-mediated interaction as well as on torsion gravity are also derived and compared with previous work performed at different length scales. Our constraints benefit from the high controllability of the experimental system which contained only two trapped particles. It therefore suggests a useful new platform for exotic particle searches, complementing other experimental efforts.

Using geoelectrons to search for velocity-dependent spin-spin interactions

We use the recently developed model of the electron spins within Earth to investigate all of the six possible long-range velocity-dependent spin-spin interactions associated with the exchange of an ultralight (mz'<10(-10) eV) or massless intermediate vector boson. Several laboratory experiments have established upper limits on the energy associated with various fermion-spin orientations relative to Earth. We combine the results from three of these experiments with the geoelectron-spin model to obtain bounds on the velocity-dependent interactions that couple electron spin to the spins of electrons, neutrons, and protons. Five of the six possible potentials investigated were previously unbounded. In the long-range limit we have improved the bound on the sixth potential by 30 orders of magnitude.

Limits on exotic long-range spin-spin interactions of electrons

We surrounded a rotating torsion pendulum containing 9.8×10(22) polarized electrons by 2 or 4 stationary sources, each with a net spin of 6.0×10(24) polarized electrons. Multiple source configurations gave sensitivity to hypothetical dipole-dipole, spin-dot-spin, and spin-cross-spin exchange interactions mediated by bosons with masses up to 20 μeV. For bosons with masses ≤0.1 μeV our null results for the dipole-dipole, spin-dot-spin, and spin-cross-spin forces imply 1σ upper limits on (g(P)(e))(2)/(ħc), (g(A)(e))(2)/(ħc) and (g(V)(e)g(A)(e))/(ħc) of 2.2×10(-16), 3.8×10(-40), and 1.2×10(-28), respectively. We also constrain, for the first time, any possible linear combination of static spin-spin interactions. In this case our upper limits relax to 5.6×10(-16), 9.8×10(-40), and 1.2×10(-28), respectively.