Quantum trajectories in spin-exchange collisions reveal the nature of spin-noise correlations in multispecies alkali-metal vapors

Abstract

Spin-exchange collisions in alkali vapors underly several fundamental and applied investigations, like nuclear structure studies and tests of fundamental symmetries, ultra-sensitive atomic magnetometers, magnetic resonance and bio-magnetic imaging. Spin-exchange collisions cause loss of spin coherence, and concomittantly produce spin noise, both phenomena being central to quantum metrology. We here develop the quantum trajectory picture of spin-exchange collisions, consistent with their long-standing ensemble description using density matrices. We then use quantum trajectories to reveal the nature of spin-noise correlations that spontaneously build up in multi-species atomic vapors, frequently utilized in the most sensitive spin measurements.

Spin noise correlations in multispecies hot atomic vapors

“…We analyse in detail spin-noise correlations between the two species and we find that even in equilibrium the two atomic systems share and exchange spin-noise correlations that build-up as a result of the spin-exchange interaction. We observe a coherence transfer between the two vapors that is more evident in small magnetic fields and we find that a positive spin-noise correlation at τ = 0 in agreement with the predictions of [89,100,118].…”

“…W e have developed and performed a precision experiment with the aim to study spin-noise correlations that spontaneously build-up due to rapid spinexchange collisions in a vapor cell containing dual-species alkali vapors at room temperature and above. The 87 Rb- 133 Cs experiment has interestingly shown non-zero spinnoise correlations leading to the conclusion that spin-exchange collisions in dual-species can generate and sustain spin-spin correlations as it has been demonstrated recently in [83,100] but also theoretically in [89,118].…”

“…Deeper understanding of spin noise and its relation to the collisional relaxation processes [85][86][87] paves the way towards improving quantum enhanced metrology in hot vapor systems [88][89][90][91]. Some of the modern applications of spin noise spectroscopy in hot vapors are: measurement of zero-field spin noise using magnetic pulses [92], measurement of higher order spin noise like alignment noise [93,94], spin noise measurements with time-dependent magnetic fields [95,96], demonstration of quantum random number generator using spin noise [97], effects of atomic diffusion on the spin noise spectrum [98,99] and dual-species spin noise measurements [100][101][102][103][104].…”

“…At higher magnetic fields, the fast spin precession averages out the exchange correlations. These effects have been also revealed using a formal quantum-trajectory picture of SE collisions [89] that allows the production of spin-noise from first principles, instead of using the phenomenological Bloch equations. The model is presented in detail in later chapters.…”

Quantum Dynamics of Collective Spin States in a Thermal Gas

“…Non-classical phenomena involving collective spin states, such as transfer of quantum correlations between nonoverlapping light beams by atomic motion [29][30][31], call for a quantum description of the thermal motion. For spinexchange collisions, which are an outcome of thermal motion, such a quantum description has received much recent attention [32][33][34][35][36][37][38]. However, the more direct consequences of thermal motion, namely the stochasticity of the spatial dynamics in the bulk and at the system's boundaries, still lack a proper fullyquantum description.…”