Low-noise Current Source Systems And Their Applications In Cold Atom Experiments

The 1997 Nobel Prize-winning laser cooling technology opened the way to investigating cold atom physics.Cold atom physics and technology develop fast in the past twenty years.The 2001,2005,2012 Nobel Prizes are developments of cold atom related technologies and applications.Quantum memory implemented with cold atom can be used in quantum communication and quantum computaion;quantum simulation with ultra-cold atom can be used to investigate the evolution phenomena of condensed matter.Along with laser and radio frequency,the magnetic field which causes the energy levels of atoms to spilt,is an important way to control cold atom.Magnetic fields are produced by injecting currents into coils.Analog-control current source is needed to generate different waveforms of magnetic fields;precise magnetic field is implemented with low noise current;some physical procedures need high bandwidth of the current.General-purpose commercial current sources have low bandwidth and large noise and can not be used in experiments like ultra-cold quantum simulation in optical lattices,Bose-Fermi superfluid mixture,which have high demand on the magnetic field and current.Therefore,to meet special demands for magnetic control,we develop three low-noise current sources:(1)Low noise current on the level of 100 Amperes are needed in magnetic transfer,radio frequency evaporative cooling,single layer slice of atoms.So we develop a large current control system based on IGBT:IGBT is used to regulate the current while high precision current transducer is used to measure current for feedback.The error signal,produced by PI calculation of input signal and feedback signal,is used to control the gate voltage of IGBT.Thus an analog control current source with 6 ppm relative current noise is realized.(2)Low-noise high-bandwidth bipolar current source on the level of 10 Amperes are needed in tuning the dipole-dipole interaction in a quantum gas and active compensation of stray magnetic field.So we develop a bipolar current source:16 A bipolar current output is implemented with a power operational amplifier which have high drive capability to drive an inductive load.We use two-stage structure,i.e.implementation PI calculation with an ultra-low noise operational ampilifier before the power operational amplifier output stage.Thus ultra-low output current noise is realized.By changing PI parameters,the circuit can adapt to different inductive loads and system bandwidth can be changed.Relative current noise of our bipolar current source is less than 5 ppm and bandwidth can be adjusted from 2 kHz to 10 kHz.(3)Compact mobile atomic interferometer system need low power consumption,small volume current system,in which the bias magnetic field current need low current noise,gradient magnetic field and compensation magnetic field need to be swtiched off fast.So we develop a current source system for atomic interferometer:it is developed on the design of bipolar current source.We lower the supply voltage to have low power consumption,simplify the circuit and integrate five current demands into a small 1U box.We replace power operational and current sense resistor for low outout current noise and low leakage current.By adding switch to integration capacitor and MOSFET to the output stage,fast switch on and off of the current without overshoot is realized,which satisfies the demands of atomic interferometer.All three current source systems are carefully tested and applied to experiments.The current sources overcome the problems of commercial current sources,gurantee the progress of experiments and provide more choices for new experiment design.