Reviewed by Lexie CornerDec 12 2024
In a new study published in Physical Review Letters, physicists from Northwestern University have introduced an exceptionally sensitive tool that amplifies incredibly weak signals by 1,000 times—an improvement of 50 times over previous capabilities.
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. Image Credit: Northwestern University
If dark matter exists, its interactions with regular matter are so faint that even the most sensitive detectors have struggled to detect them.
One of the key technologies used in this study is the atom interferometer, a highly precise instrument that uses light to manipulate atoms and measure extremely small forces. However, unlike previous atom interferometers, which were limited by imperfections in the light, this new tool is designed to self-correct for those flaws, enabling it to achieve unprecedented accuracy.
This breakthrough, which brings nearly imperceptible signals into a measurable range, could be a game-changer for scientists searching for ultra-weak forces from phenomena like dark matter, dark energy, and gravitational waves—especially in previously unexplored frequency ranges.
Dark matter is somewhat of an embarrassing problem. It is a weird dichotomy because the ordinary matter that we encounter in everyday life, we understand extremely well. But that only makes up 15 % of the matter in the universe. We don’t know the nature of the rest, which makes up most of the matter in the universe. So, it is just a big incompleteness. Atom interferometers could potentially have a big impact in searching for this kind of dark matter.
Timothy L. Kovachy, Assistant Professor, Weinberg College of Arts and Sciences, Northwestern University
Timothy L. Kovachy is also a member of the Center for Fundamental Physics.
What is an Atom Interferometer?
Atom interferometers were developed in 1991 and rely on the principle of superposition, a key concept in quantum mechanics that allows a particle to exist in multiple states at once. In these devices, an atom behaves like a wave, simultaneously traveling in two directions. Using lasers, the atom is split into two waves, which then travel along separate paths before recombining.
When the waves eventually recombine, they form a unique pattern, much like a fingerprint, that reveals the forces acting on the atoms. Scientists can analyze this pattern to measure incredibly small forces and accelerations that would otherwise be invisible.
Kovachy added, “Atom interferometers are really good at measuring small oscillations in distances. 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.”
The Problem with Current Instruments
At such a small scale, even the slightest disruption can throw off the whole experiment. Minor imperfections—like a single photon—can interfere with the wave-like atom’s path, shifting it by as little as one centimeter per second and causing errors in the resulting interference pattern.
“Photons can’t carry that much momentum, but atoms also don’t have that much mass. 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 ten pulses, the signal was just gone,” Kovachy explained.
‘Self-Correcting’ System
To address this issue, Kovachy and his team developed a new approach for carefully coordinating the sequence of laser pulses. By incorporating machine-learning techniques, the technology can "self-correct" for flaws in individual light pulses. The researchers fine-tuned the waveforms of the pulses, reducing the overall impact of any errors in the experimental setup.
After running simulations, Kovachy’s team built the experiment in the lab. The results were impressive: they found that the signal was amplified by 1,000 times.
Kovachy concluded, “Before, we could only do ten laser pulses; now we can do 500. 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.”
Journal Reference:
Wang, Y. et. al. (2024) Robust Quantum Control via Multipath Interference for Thousandfold Phase Amplification in a Resonant Atom Interferometer. Physical Review Letters. doi.org/10.1103/PhysRevLett.133.243403