Full-loop Stern-Gerlach Interferometer

Gaurav Kumar


The Stern-Gerlach effect can be defined as quantization of the special orientation of an angular momentum. It was discovered a century ago. Otto Stern gave the concept of the experiment in 1921 while Walther Gerlach conducted the experiment over his concepts and successfully discovered the Stern-Gerlach effect in the year 1922. The name Stern-Gerlach effect depicts the contributions of both the scientists.

The experiment demonstrated that an atomic scale system includes quantum properties. The figure given below represents the original Stern-Gerlach experiment in which silver atoms are projected over a spatial magnetic field. The magnetic field deflects the silver atoms as they hit the detector screen made up of a glass slide. Deflection occurs in the non-zero magnetic moment particles in a straight line or path. The detector screen represents the accumulated discrete points instead of continuous distribution. Through this, we can easily understand the explanation of quantized spin. The above experiment was mainly conducted to explain the reality of the quantization of angular momentum in each and every atomic-scale system.

File:Stern-Gerlach experiment svg.svg
Stern-Gerlach Experiment
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Stern-Gerlach Experiment:

The Stern-Gerlach effect is effectively used in our modern science and development and is considered the role model for quantum mechanics. When these freely propagating atoms are exposed to the gradients of macroscopic magnet defines the science behind the quantum process. However, developing a full-loop Stern-Gerlach interferometer has been a formidable challenge still in our modern science. Several theoretical studies explain the reasons for this. Here in this article, we will understand the important facts behind the first full-loop Stern-Gerlach interferometer that is based on highly précised magnetic fields that originates from the atomic chip.

This atom chip efficiently ensures coherent operations along with strict constraints as explained in the previous analysis of the experiment and theory. As we have achieved such a high level of précised control over magnetic field gradients can be considered as a milestone in historical science and development. These magnetic gradients are considered to facilitate fundamental as well as technological application expectations. The application may be used in probing the interface of gravity as well as quantum mechanics. However, the experiment was conducted on a single atom using the Stern-Gerlach effect. This would be beneficial for various challenges in the future for implementing macroscopic objects being doped within a single spin. This success will surely open several doors for a new age of fundamental probes that includes the realization of a full-loop Stern-Gerlach interferometer forming the base for interfaces of gravity and quantum mechanics.

The Stern-Gerlach effect resulted in the discovery of new ideas for a full-loop Stern-Gerlach interferometer that consists of a beam of silver atoms projected over the macroscopic magnetic field gradient. However, according to the theories of Winger, Bohm, and Heisenberg, it is impossible to design such précised macroscopic device that is capable of reversing the splitting process involved in the experiment. But Stern and Gerlach obtained a 95% contrast full-loop SG interferometer using an accurate magnetic field over the atomic chip. This could be better understood by the below-given figure that represents the longitudinal full-loop SG interferometer in accordance with framing the center-of-mass.

The longitudinal full-loop Stern-Gerlach interferometer in the center-of-mass frame

The total duration for the operation of the interferometer is considered as 2T that consists total four magnetic gradient pulses. The obtained signals are constructed from the spin fringes. This configuration can be used in interferometer for macroscopic objects for testing various aspects of gravity. This can be better understood by the below given figure that represents the laboratory frame of the longitudinal full-loop Stern-Gerlach interferometer.

The experiment begins with projecting BEC of 104 87Rb silver atoms obtained from the magnetic field towards the given atom chip. Then a full-loop Stern-Gerlach interferometer is applied with the help of four magnetic gradient pulses. The direction of acceleration during second and third magnetic gradient pulses is just opposite to the acceleration during the first and fourth magnetic gradient pulses. The population signal can be obtained using the second pulse of the spin population measurement. The exact duration for each and every gradient pulses is totally dependent over the delay time, scheme used and the distance from the atom chip. We are then required to optimize two different independent parameters like minimizing the final relative position as well as minimizing the final momentum in the experiment. This can be better understood by the below given figure that represents full-loop optimization procedure.

Process of full-loop optimization


The above experiment results in recombination of the final momentum and position since they cause loss of visibility in outcomes. The testing of various aspects of gravity can be done by using the full-loop Stern-Gerlach interferometer. States of macroscopic quantum is a very big challenge for a long period of time. The Stern-Gerlach experiment mainly focuses on the super-positioning of a macroscopic object. The range of experiments is very wide from detecting the gravitational waves towards testing the quantum gravity. The feasibility of the above can be understood very efficiently using the full-loop Stern-Gerlach interferometer over the macroscopic body.

When we consider gravity, the contribution of the experiment relies on measuring the local acceleration due to gravity, g. This will enable the verification of super-positioned macroscopic objects. The second contribution of the above experiment is in testing gravity modifications in very short ranges.

The main focus of the experiment is on required parameters for the Stern-Gerlach effect that includes acceleration and précised coherence and splitting lengths. The coherence length is comparatively shorter as it should be for pure condensation. Physicists have successfully designed the Stern-Gerlach interferometer over an atom chip. This quantum interferometer can be efficiently used for exploring fundamental quantum theory. Several experiments were conducted over photons for the interferometer, but this time physicist successfully conducted the Stern-Gerlach effect over an atom. This can be considered the first milestone in the history of physics and can be efficiently used for detecting gravity. This quantum sensor can detect several other measurements that are needed to be explored in the future.




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