基于Rydberg原子的高灵敏微波探测与通信

利用Rydberg原子作为微波传感器实现了微弱场的测量与通信.在铯原子蒸气池中,相向传输的探测光(852 nm)和耦合光(510 nm)与铯原子相互作用形成阶梯型三能级电磁感应透明光谱,用于实现Rydberg原子的光学探测.频率约为2.19 GHz的强微波场作为本地场(E_L),共振耦合相邻的两个Rydberg能级|68D_5/2>和|69P_3/2>,与具有一定失谐δf的待测微弱信号场(E_s)同时作用于Rydberg原子.Rydberg原子作为微波混频器可直接读出两束微波的差频信号,实现待测信号场的高灵敏探测,对应的最小测量值为E₀=1.7μV/cm,频率分辨率小于1 Hz.在此基础上,对微弱信号场进行编码,实验上很好地还原了加载到微波弱场上的基带信号,测量的传输带宽达200 MHz,实现了微弱场条件下的通信.

High-sensitive microwave sensor and communication based on Rydberg atoms

We present a high-sensitivity weak microwave measurement and communication technology by employing the Rydberg beat technique.The Rydberg cascade three-level system is composed of a cesium ground state 6S_1/2,an excited state 6P_3/2,and a Rydberg state nD_5/2in a room-temperature cesium cell.A two-photon resonant Rydberg electromagnetic induced transparency(EIT)is used to optically detect the Rydberg level,in which a weak probe laser is locked at the resonant transition of|6S_1/2>→|6P_3/2>,and a strong coupling laser drives the transition of|6P_3/2>→|nD_5/2>.Both lasers are locked with a high-precision Fabry-Perot cavity.Two E-fields are incident into the vapor cell to interact with Rydberg atoms via a microwave horn,one is a strong microwave field with frequency 2.19 GHz,acting as a local field(E_L)and resonantly coupling with two Rydberg energy levels,|68D_5/2>and|69P_3/2>,and the other is a weak signal field(Es)with frequency differenceδf,interacting with the same Rydberg levels.The wave-absorbing material is placed around the vapor cell to reduce the reflection of microwave field.In the presence of the local field,the Rydberg atoms are employed as a microwave mixer for reading out the difference frequencyδf oscillation signal,which is proportional to the amplitude of weak signal field.The minimum detectable field of E₀=1.7μV/cm is obtained when the lock-in output reaches the base noise.We also measure the frequency resolution of the Rydberg mixer by changing theδf with fixed fref,thus achieving a frequency resolution better than 1 Hz.For neighboring fields with 1 Hz away from the signal field,an isolation of 60 dB is achieved.Furthermore,we use the Rydberg atom as an antenna to receive the baseband signals encoded into the weak microwave field,demonstrating that the receiver has a transmission bandwidth of about 200 MHz.The demonstration of sensitivity of Rydberg atoms to microwave field is particularly useful in many areas,such as quantum precise measurement and quantum communications.In general,this technique can be extended to the detection of electromagnetic radiation from the radio-frequency regime to the tera-hertz range and is feasible for fabricating a miniaturized devices,thereby providing us with a way to receive the information encoded in tera-hertz carriers in future work.