Quantum metrology with atom chip

The goal of quantum metrology is to increase the sensitivity of physical fields measuring. It can be achieved by using quantum mechanics effects such as interferometry of quantum states, squeezing, etc. Quantum sensors used as instruments for high sensitivity measurements reached outstanding results in laboratory conditions. There is currently a growing trend towards outdoor experimentation. The main development trend is the decreasing of dimensions and power consumption of quantum sensor in comparison with used sensors in classical approaches. Increasing sensitivity of outdoor sensors will allows us to move to the next technological level.
Among various types of quantum sensors, the sensors using neutral atoms are promising. To increase the quantum senser sensitivity the approach of atomic state interference is used.
Atom interferometry is considered as a platform for high precision fundamental experiments and for solving numerous applied problems [1]. For instance, microwave atomic clock used interference pattern of Ramsey fringe for high stability of frequency standards. The precision of quantum sensors is limited by the quantum projection noise. Therefore, the number of atoms forming the interference pattern is the cornerstone of quantum sensor. To reach high precision of quantum sensors based on atom interferometry the effective source of cold atoms is necessary. There are three types of atoms sources can be used for atom interferometry: (1) atomic beam; (2) cold atoms in magneto-optical trap (MOT); (3) ultracold atoms trapped on atom chip. The use of the first type of atom source leads to quantum sensors of large spatial dimensions. Cold atoms from MOT are actively used in quantum sensors, for instance, in atomic gravimeter [2,3]. The drawback of MOT as an atomic source is the temperature of atomic ensemble. In case of sub-Doppler cooling the temperature is about several microkelvins. Lower temperatures require evaporative cooling. Unfortunately, MOT is not suitable for evaporative cooling, which is usually done in a magnetic trap.
The atom chip operation is based on a cold atom trapping near the microwire. In this case a high gradient of magnetic field can be achieved relatively easy. Approach for ultracold atom source sensor baser on atom chip has been demonstrated with high bandwidth [4]. Until now, most demonstrated atom chips have been technically sophisticated, with multiple layers of microwires to cool and trap atoms. We demonstrated single-layer atom chip which can be used as atom source for atom interferometry and quantum sensors [5]. The new type of single-layer atom chip developed, which makes it possible to increase the number of atoms up to 5?107 [6]. The magnetic trapping of atoms gives the possibility to use evaporative cooling to reach the temperatures below 1 mkK. It gives us the possibility of coherent manipulations with atomic ensemble.
The study was supported by the Russian Science Foundation, grant No. 23-22-00255.
References
[1] R. Geiger, et al., AVS Quantum Sci. 2, 024702 (2020).
[2] V. Menoret, et al., Sci Rep 8, 12300 (2018).
[3] Pan-Wei Huang, et al., Metrologia 56, 045012 (2019).
[4] J. Rudolph, et al., New J. Phys. 17, 065001 (2015).
[5] A.E. Afanasiev, et al., Optics & Laser Technology, 148, 107698 (2022).
[6] P. Skakunenko, et al., Chinese Optics Letters, 22, 060201 (2024).