Given the assumption that dark matter is real, its interactions with regular matter are so subtle that even the most sensitive instruments cannot detect them.
In a new study, Northwestern University physicists have unveiled an extremely sensitive new device that amplifies faint signals by 1,000 times — a 50-fold enhancement compared to previous capabilities.
Called an atom interferometer, this highly precise instrument manipulates atoms using light to measure exceptionally minute forces. However, unlike traditional atom interferometers, which are constrained by imperfections in the light, this new device self-corrects for those imperfections, achieving unprecedented levels of accuracy.
By elevating undetectable signals to detectable levels, this technological breakthrough could assist researchers seeking ultra-weak forces generated by a range of elusive phenomena, such as dark matter, dark energy, and gravitational waves across uncharted frequency bands.
“Dark matter is somewhat of an embarrassing problem,” said Northwestern’s Timothy L. Kovachy, who led the work. “It’s a weird dichotomy because we understand the ordinary matter that we encounter in everyday life 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’s just a big incompleteness. Atom interferometers could potentially have a big impact in searching for this kind of dark matter.”
Introduced in 1991, atom interferometers represent a groundbreaking advancement that harnesses the principle of superposition from quantum mechanics, allowing particles to exist in multiple states simultaneously. In these devices, atoms behave like waves, navigating two distinct paths at once.
An atom interferometer employs lasers to divide a wave-like atom into two waves, which then travel along different routes before being brought back together.
Upon recombination, these waves produce a distinctive interference pattern akin to a unique fingerprint, which unveils the unseen forces acting upon the atoms. Through careful analysis of this pattern, scientists are empowered to measure incredibly subtle and imperceptible forces and accelerations.
“Atom interferometers are really good at measuring small oscillations in distances,” Kovachy said. “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 such small waves, it only takes a slight disruption to affect the whole experiment. Even the smallest flaw can result in mistakes in the interference pattern. For instance, a single photon can throw the wave-like atom off its trajectory—altering its path with a speed of one centimeter per second.
“Photons can’t carry that much momentum, but atoms also don’t have that much mass,” Kovachy explained. “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.”
To address this issue, Kovachy and his team devised a novel technique to meticulously organize the timing of laser pulses. Utilizing machine-learning methods, their approach “self-corrects” for the flaws found in the individual light pulses. By managing the waveforms of the laser pulses, the researchers mitigated the overall impact of errors resulting from 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 imperfections in each one. That could allow us to unlock the full potential of atom interferometry.”
Journal reference:
Yiping Wang, Jonah Glick, Tejas Deshpande, Kenneth DeRose, Sharika Saraf, Natasha Sachdeva, Kefeng Jiang, Zilin Chen, and Tim Kovachy. Robust Quantum Control via Multipath Interference for Thousandfold Phase Amplification in a Resonant Atom Interferometer. Physical Review Letters, 2024; DOI: 10.1103/PhysRevLett.133.243403