The School of Electronics has made a new breakthrough in quantum sensing technology of two-dimensional electromagnetic force

Force is the basic object
of study in physics.
The measurement of weak forces has always been a key means to verify basic physics and discover new physics, such as discovering new physics beyond the standard model, measuring vacuum fluctuations, detecting gravitational waves, and exploring dark matter
.
The weak force determines our understanding of the fundamental laws of
physics from the micro to the macro.
At the same time, force measurement is directly used in many fields, and it is widely used in the characterization of material surface morphology, gravimeter, inertial navigation, etc
.
The accuracy of weak force measurement directly determines the level of our understanding of basic science and the accuracy
of measurement in technical applications.

Traditionally, we measure force
through the mechanical motion of an object.
We need to measure the spatial coordinates of the beginning and end states of the object during the application of force to calibrate the acceleration
.
The results show that the measurement method cannot break through a standard quantum limit
due to the "Heisenberg uncertainty principle".
To this end, after long-term efforts, the international scientific research team has explored different experimental systems, improved the force measurement technology, and greatly improved the sensitivity
of force measurement.
Technical details are maximized in a variety of different experimental systems to improve the sensitivity
of force measurement.
Recently developed sensing technology for electrostatic field forces by single ions has achieved measurement sensitivities
of 1E-19 N/Hz.

Figure 1 The experiment completes the highly sensitive quantum measurement of two-dimensional electromagnetic force by forming quantum matter waves from atoms in the triangular optical lattice

The joint R&D team of Peking University and Fudan University has been committed to the research of cold atomic quantum systems for a long time, and has developed a number of original technologies for the external state control of cold atoms in the optical lattice, which can carry out high-precision quantum control
of quantum matter waves formed by hundreds of thousands of atoms.
The method of separating the real space motion and momentum space motion of matter waves based on optical lattice technology was used to complete the control and measurement of quantum matter wave vectors (as shown in Figure 1).

At the same time, Bragg scattering of matter waves in the optical lattice gives precise two-dimensional coordinates
for calibrating the size and direction of the wave vector of substances.
This quantum measurement technique can directly and accurately measure the accumulation of material waves under the action of force, without the need to measure the spatial position change
of atoms.
This technique establishes a direct connection between force and Planck's constant through quantum matter waves, and we do not need to calibrate physical quantities such as atomic mass, atomic number, atomic magnetic moment, etc.
, and we will not be affected
by the measurement uncertainty of these physical quantities.
In the experiment, the sensitivity of quantum matter waves to force perception reached 2E-26N/Hz, breaking through the above standard quantum limit by nearly an order of
magnitude.
The team conducted thousands of quantum matter wave repeat experiments and completed the measurement of a very weak force, and statistical analysis of large-scale data showed that the measurement accuracy reached 2E-28N, which is equivalent to the strength
of the van der Waals force between atoms at the millimeter scale.

Magazine cover

The results were published in Science Bulletin in November 2022 and were selected as the cover story
of the magazine.
Xinxin Guo and Zhongcheng Yu are co-first authors of doctoral students from the School of Electronics of Peking University, Professor Xiaopeng Li of Fudan University, Xibo Zhang of the Center for Quantum Materials Science of the School of Physics, Peking University, and Professor Xiaoji Zhou of the School of Electronics are co-corresponding authors
.

This research was supported
by the National Natural Science Foundation of China, the Ministry of Science and Technology, the Shanghai Municipal Science and Technology Commission, and the Ministry of Spatial Administration.