Scientists at Northwestern University have developed a groundbreaking interferometer that amplifies faint signals by 1,000 times, making it 50 times more sensitive than previous models. This tool uses laser pulses to manipulate atoms and corrects for imperfections that have long hindered precision. With this innovation, researchers hope to detect ultra-weak forces from dark matter, dark energy, and gravitational waves.
A cloud of cold, trapped strontium atoms hovers inside the atom interferometer. Invented in 1991, atom interferometers take advantage of superposition, a fundamental principle in quantum mechanics that a particle can exist in multiple states simultaneously. In this case, an atom behaves like a wave that exists along two paths at once.
Lasers split a wave-like atom into two waves, send those waves on two different paths, and then recombine them. When the waves recombine, they create a pattern, which is like a fingerprint that reveals forces acting on the atoms. By studying this pattern, scientists can measure tiny, invisible forces and accelerations.
“Atom interferometers are really good at measuring small oscillations in distances,” said Timothy L. Kovachy, who led the work. “We don’t know how strong dark matter is, so we want our instruments to be as sensitive as they can be.
Because we haven’t ‘seen’ dark matter yet, we know its effects must be pretty weak.”
When working with waves this tiny, even the tiniest imperfection can lead to errors in the interference pattern. A single error can derail the wave-like atom’s path, kicking it off-course with a velocity of one centimeter per second.
Amplifying dark matter detection signals
“If we lose one atom, that doesn’t seem like the end of the world. But if we apply many laser pulses of light to boost the atom interferometer’s ability to amplify small signals, those errors will compound. And they will compound fast.
In practice, we saw that after about 10 pulses, the signal was just gone,” Kovachy explained. To overcome this challenge, Kovachy and his team developed a new technique to carefully orchestrate the sequence of laser pulses. The method “self-corrects” for the imperfections in individual pulses of light.
By controlling the waveforms of laser pulses, the researchers reduced the overall effect of errors caused by imperfections in the experimental setup. After testing the model in simulations, Kovachy’s team built the experiment in the lab. The experiments verified the signal was amplified by 1,000 times.
“Before, we could only do 10 laser pulses; now we can do 500,” Kovachy said. “This could be game-changing for many applications. The atom interferometer as an entire entity ‘self-corrects’ for the imperfections in each laser pulse.
We can’t make each laser pulse perfect, but we can optimize the global sequence of pulses to correct for imperfections in each one. That could allow us to unlock the full potential of atom interferometry.”
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