Physicists make laser beams visible in vacuum
Date:
August 25, 2021
Source:
University of Bonn
Summary:
A beam of light can only be seen when it hits matter particles
and is scattered or reflected by them. In a vacuum, however,
it is invisible.
Physicists have now developed a method that allows laser beams to
be visualized even under these conditions. The method makes it
easier to perform the ultra-precise laser alignment required to
manipulate individual atoms.
FULL STORY ==========================================================================
When individual atoms interact with each other, they often exhibit unusual behavior due to their quantum behavior. These effects can, for instance,
be used to construct so-called quantum computers, which can solve certain problems that conventional computers struggle with. For such experiments, however, it is necessary to maneuver individual atoms into exactly the
right position. "We do this using laser beams that serve as conveyor
belts of light, so to speak," explains Dr. Andrea Alberti, who led the
study at the Institute of Applied Physics at the University of Bonn.
==========================================================================
Such a conveyor belt of light contains countless pockets, each of which
can hold a single atom. These pockets can be moved back and forth at will, allowing an atom to be transported to a specific location in space. If
you want to move the atoms in different directions, you usually need many
of these conveyor belts. When more atoms are transported to the same
location, they can interact with each other. In order for this process
to take place under controlled conditions, all pockets of the conveyor
belt must have the same shape and depth. "To ensure this homogeneity,
the lasers must overlap with micrometer precision," explains Gautam
Ramola, the study's lead author.
A bean in a soccer stadium This task is less trivial than it sounds. For
one thing, it requires great accuracy. "It's kind of like having to aim
a laser pointer from the stands of a soccer stadium to hit a bean that's
on the kickoff spot," Alberti clarifies.
"But that's not all -- you actually have to do it blindfolded." This
is because quantum experiments take place in an almost perfect vacuum,
where the laser beams are invisible.
The researchers in Bonn therefore used the atoms themselves to measure
the propagation of laser beams. "To do this, we first changed the laser
light in a characteristic way -- we also call it elliptical polarization," Alberti explains. When the atoms are illuminated by a laser beam prepared
in this way, they react changing their state in a characteristic
way. These changes can be measured with a very high precision. "Each
atom acts like a small sensor that records the intensity of the beam,"
Alberti explains. "By examining thousands of atoms at different locations,
we can determine the location of the beam to within a few thousandths
of a millimeter." In this way, the researchers succeeded, for example,
in adjusting four laser beams so that they intersected at exactly the
desired position. "Such an adjustment would normally take several weeks,
and you would still have no guarantee that the optimum had been reached," Alberti says. "With our process, we only needed about one day to do this." ========================================================================== Story Source: Materials provided by University_of_Bonn. Note: Content
may be edited for style and length.
========================================================================== Journal Reference:
1. Gautam Ramola, Richard Winkelmann, Karthik Chandrashekara,
Wolfgang Alt,
Peng Xu, Dieter Meschede, Andrea Alberti. Ramsey Imaging of
Optical Traps. Physical Review Applied, 2021; 16 (2) DOI: 10.1103/
PhysRevApplied.16.024041 ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2021/08/210825143048.htm
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