# Atomic Receiver by Utilizing Multiple Radio-Frequency Coupling at Rydberg States of Rubidium
## 2 Methods
### Wireless Reception of Image Data  
Based on different data transfer rates, more experiments were carried out to test the capability of data retrieving by the proposed atom-based FDM receiver. The transmitted images (letters \"A\", \"B\", \"C\", and \"D\") are 36 by 36 pixel Portable Network Graphics (PNG) with lossless compression. Image data is encoded into a one-dimensional digital flow from corresponding two-dimensional array data, and then transmitted in different channels. Actually, images with different pixel sizes and formats can be used. The experimental probe laser power was 30 \(\mu\)W, whereas the coupling laser power was 100 mW. The RF-carrier frequency of the CH1 was with a resonance frequency of 10.22 GHz and a power of 3 dBm. The RF-carrier frequency of the CH2 had a detuning frequency of 10.25 GHz and a power of 4 dBm. To achieve the port matching, the cable attenuation was calibrated before conducting the experiment. Moreover, power adjustment of the two channels made the actual antenna feeding power from the two channels identical, and both carriers were modulated by an external signal source. In the experiment of receiving FM signals, CH1 and CH2 transmitted the images of letters \"C\" and \"D\", respectively. The FM modulation depth in the experiment was 30 MHz. Figure 5 shows an image recovered by the proposed atomic receiver at various data transfer rates. It is clear that, with both modulation modes, the experimental results demonstrated an acceptable performance with a data transfer rate up to 500 kbps.  
In digital transmission, bit error ratio (BER) was used to study the probability of receiving bits of data stream on the communication channel, which is often due to noise, interference, distortion, or bit synchronization error. In our experiment, a classical definition of BER is used, that is, the number of bit errors divided by the total transferred bits. BER values of different channels and modulation are shown in Figure 6. Generally, BER for data transfer in the detuning carrier was higher than that in the resonance situation. In the experiment of receiving the AM signal, the BER of the two channels can be kept at nearly 0 when the data transfer rate was less than 100 kbps. For receiving FM signals, the BER was close to 0 when the data transfer rate was less than 300 kbps, and even with the data transfer rate going up to 500 kbps, the BER increased to approximately 2%.  
Figure 4: Interchannel interference performance of FM communication. (**a**) SNR of two channels changes with \(\Delta_{RF}\). (**b**) Received signals when \(\Delta_{RF}\) is 0, 5 and 10 MHz respectively.  
In the latest released technical specification document (3 GPP TS 23.107 V15.0.0) within the 3 rd-Generation Partnership Project (3 GPP), the BER value ranges for Universal Mobile Communication System (UTMS) bearer service attributes are recommended. For some applications of Class 2 bits, a higher BER (5%) might be feasible. The experimental results show that the maximum acceptable data transfer rate of both AM and FM is ~200 kbps, whereas their maximum BER is less than 5%.