| Cold atom gas is small,similar to "static" well coherent,relatively fixed in vacuum.When cold atoms are in the light field,magnetic field or microwave field,they are very easy to be manipulated,so the cold atoms provide a good research platform for a variety of quantum physics experiments.When laser or microwave manipulates cold atoms,their amplitude,frequency and direction need to be flexibly changed,so high-precision,high-resolution laser and microwave in cold atom experiments is particularly important.When lasers are used to manipulate cold atoms,the parameters of the laser(eg frequency and intensity)need to be stabilized,scanned or switched.It is common practice to perform similar operations on the RF signal and then transfer these operations to the laser via an acousto-optic modulator(AOM).Using microwave to manipulate cold atoms is the same,usually the RF signal is first gotten,and then the antenna radiation is used to produce the microwave with the same frequency.Therefore,most of the time,the laser or microwave manipulation can be converted to the RF signal regulation,so accurate stable and easy-manipulated RF signal has become a common demand for a variety of cold atom experiments.The traditional RF signal source has voltage-controlled oscillators(VCO)and standard commercial radio frequency equipments.VCO frequency accuracy and stability is not enough,and the general standard commercial RF equipments sweep speed and sweep mode are limited.For example,in cold atom optical lattice experiments,the RF source needs to perform complex operations,and the sweep speed needs to reach microseconds,the sweep accuracy needs to reach Hz.The traditional VCOs or standard commercial RF instruments are not up to the experiment claim.So for the cold atom experiments,dedicated precise agile RF sources are needed.In order to meet the specific needs of various cold atom experiments,two precise agile RF sources were designed using the principle of direct digital synthesis(DDS):DDS-400MHz precise agile RF source and DDS-6.8GHz precise agile RF source.Among them.DDS-6.8GHz RF source has two kinds of use,can be used as low frequency to 1.4GHz RF source or 6.8GHz ± 300MHz RF source.DDS-400MHz RF source is generally used to manipulate Li,K and other small atoms,and is the most widely used,the most used precise agile RF source.It has low cost,low power consumption.DDS-1.4GHz RF source can be used for other different atoms.DDS-1.4GHz RF source combined with up-conversion technology,you can extend the RF frequency to the microwave band,that is,can reach 6.8GHz ± 300MHz high frequency range.This high frequency range corresponds to the microwave can be used to couple Rb atoms.This paper synthesizes the similarities and differences of the laser and microwave requirements in various cold atom experiments,and designs a multi-function precise agile customizable swept DDS RF source.It has achieved good experiment effects in various cold atom experiments,and has helped cold atom experiments to make a lot of cutting-edge research results.The innovation of this paper is as follows:(1)Aiming at the characteristics of high frequency stability,high resolution and fast frequency hopping of the signal source,the FPGA + DDS architecture is used to design the precise agile RF source of frequency range of 400MHz and 1.4GHz.Frequency hopping time realies 80ns,to solve the cold atom experiments fine and complex control problems in the laser field and microwave field.(2)The DDS + up-conversion technology is used to realize the agile microwave source in the 6.8GHz frequency band,the frequency range is 6.8GHz ± 300MHz,and the application of quantum computation and quantum simulation experiment in the optical lattice is covered.(3)In view of the lack of strong control capability of DDS,a variable gain control circuit with high modulation bandwidth is designed,and the complex scanning can be carried out together with the frequency control.The dynamic range is 70dB and the turn-off ratio reaches-80dBc. |
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