Preparation And Application Of New Quantum Ensemble

The preparation and application of a new quantum ensemble,based on the atom-photon interaction,has significant value for quantum information science.This thesis describes two kinds of new quantum ensembles,including their preparation process and their corresponding applications.Firstly,a miniature quad-channel spin-exchange relaxation free?SERF?magnetometer has been developed.Applied to the field of mag-netoencephalography?MEG?,the sensor has been used in a steady-state visually evoked potential?SSVEP?paradigm,successfully detecting responses generated by the brain.Secondly,we have developed a cold atom ensemble with ultra-large optical depth?OD?,using a far-off resonant optical trap.A four-wave mixing?FWM?experiment has been performed in this quantum ensemble.SERF magnetometers are a new type of ultra-sensitive optically pumped atomic magnetometers,which use optical interrogation of the spin of alkali atoms to detect weak magnetic fields.Exhibiting many important qualities such as miniature size,low power consumption,and high reliability,they have the potential to replace supercon-ducting quantum interference devices?SQUIDs?,which to this day are limited by high manufacturing and maintenance costs in biomagnetic applications.With a vapor cell volume of 8×8×8 mm³,the atomic magnetometer uses a single beam for both pumping and probing of the atomic polarization.The dimensions of the sensor are 190 mm×40 mm×20 mm,and its main components are:an optical system,an alkali atom vapor cell,a coil system,a heater,and a low-noise preamplifier.We have developed a novel non-magnetic heater,which can heat the vapor cell up to 160?.It is based on a heat pipe,thus eliminating excessive noise from the heating coils.The sensor can implement multi-channel measurements and the gradiometric sensitivity is better than 6fT/Hz^1/2,which offers sufficient spatial resolution for MEG and magnetocardiography?MCG?measurements.Moreover,we have successfully observed an SSVEP response using the miniature quad-channel magnetometer.The magnetic field strength and cor-responding signal to noise ratio?SNR?of the SSVEP responses have been analyzed for different stimulation frequencies.Another new quantum ensemble described in the thesis is the cold atom ensemble with ultra-large OD.When loading the cold atom ensemble from magneto-optical trap to the far-off resonant optical trap,with a wavelength of 1064 nm,the OD is up to2857.Such setup is defined by high stability and good uniformity,as compared to a traditional two-dimensional magneto-optical trap?2D-MOT?,thus making it an ideal experimental system for quantum information and non-linear optics.Moreover,we have performed the FWM process using this quantum ensemble.The results show that the signal strength of Stokes or anti-Stokes reaches up to the?W range.The linewidth of non-classical photon pairs generated in the quantum ensemble is narrower than that in crystalline media.An obvious threshold characteristic has also been observed,which might be a non-inversion laser effect.