Jacobus Kapteyn, a Dutch astronomer, first suggested the existence of dark matter almost a century ago. When he was studying the motions of stars in galaxies, he noticed something was wrong. A galaxy is a collection of stars, dust, and gas rotating around a common central. The outer layers of the galaxy's stars were spinning at a rate that was not consistent with gravity laws. Kapteyn's hypothesis was that there might be some invisible, huge stuff in the galaxy and it could be causing the outer stars to reach the observed speeds.This hypothesis was supported by more evidence from the 1960s through the 1980s by Vera Rubin and Kent Ford. They concluded that galaxies must have six times the amount of invisible mass than visible stars, gas, and dust.Others supporting dark matter were also observed, including gravitational lensing as well as anisotropies within the cosmic microwave background. Gravitational lensing refers to the phenomenon where light beams are bent around large objects. The cosmic microwave background, which is the outer layer of our universe, is not homogeneous but rather lumpy.Uncountable masterminds have created theories and conducted experiments to find dark matter. However, no one has yet to see a particle of dark matter. Senior scientists and doctoral students, like me, continue to research dark matter. It still feels as though dark matter discovery is many centuries away, maybe even millennia.However, quantum computing has made dark matter physics possible with recent advancements. Scientists are still trying to find two types of dark matter, but they don't know if they exist. However, quantum technology might be able to help them. The first is the axion. Its existence could explain why the strong nuclear force doesn't change when you flip a particle electric charge or parity. The dark photon is the other type. These particles behave in the same way as photons, which are particles of light. However, dark photons don't have any light.Looking for axions?The theory holds that axions should move in space and time at a certain frequency. However, theorists cannot predict what frequency that frequency might be. Researchers are forced to scan a wide range of frequencies one at a time.Axion detectors convert axion signals into electromagnetic signals, much like an old radio receiver that converts radio waves to sound. The process becomes more complex when axions oscillate simultaneously at two frequencies.This could look a lot like a drunk man trying to get home after a party. They might walk three steps to one side, then take three to the other, and then turn to the left. This is one frequency on the left-right spectrum. They may also experience massive hiccups and might jump in the air at every HIC! (every four steps). This is the second frequency on the up-down spectrum.Although Axions are more sophisticated than drunk people they have two frequencies just like partygoers who have had too many drinks.These two frequencies can be combined mathematically by quadratically adding them. This is how it works: one multiplies each frequency, then adds the second frequency, and finally takes the square root.Three steps multiplied by themselves for the first frequency equals nine steps, while four steps multiplied by themselves for the second frequency equals 16 steps. Add these numbers together and we find that five steps is the square root of the nine steps squared and 16 steps squared. In our example, this is electromagnetic field quadrature.Credit: Author supplied The unique properties of quantum systems make them more efficient when searching for axions.You would normally need to test a small band of frequencies (equal one step in our example) across a wide range of frequencies (let's say one to 200 steps). This is actually even more difficult. The frequency of an axion could be between 300 Hertz to 300 billion Hertz. This is a huge, vast area to cover. This range could be covered in as little as 10,000 years, based on the current method. We can only test one bandwidth at a given time.The so-called uncertainty principle limits this bandwidth. In our example of party-going, an observer might get drunk and miscount every frequency by two steps. Two steps might be missed and they may calculate the square root 12, which is approximately two steps. They might also calculate the square root five squared plus sevensquared, which would take about eight steps. This gives you a bandwidth of six steps. If the observer wanted to scan the range from one to 200 steps they would need to measure 33 times. However, they will not need to measure frequency as often as they have bandwidth.The process of quantum squeezing allows for the expansion of this bandwidth. One can redistribute uncertainties by borrowing superconducting circuits directly from quantum computers.The drunk observer may be able to count up-down frequencies with a precision of one step but might miss the left-right frequency by three. The square root of one squared plus zero could be one step. However, he might miss the left-right frequency by three steps. This means that the bandwidth has increased by one step and the observer now only needs to measure 28 rather than 33 times.This protocol was implemented by the HAYSTAC consortium, which includes researchers from Yale University, University of CaliforniaBerkeley and Lawrence Berkeley National Laboratory. They have already reduced the observation time by quantum squeezing. It was previously 10,000 years. They believe that they can make the search for axions 10 times faster with further improvements.Allow dark photons to travel through wallsFermilab scientists are working to speed up the search for dark photosns. They fill one superconducting microwave cavity (with photons) and leave the other empty. The theory is that a small percentage of these photons will spontaneously become dark photons. Because dark photons are able to travel through walls (yes it is wild stuff), some will end up in the second cavity that scientists have created. Scientists can detect a small percentage of these dark photons turning back into regular photos.These photon-detectors have two issues. They sometimes return false positives. They indicate that they have found a photon, but in reality there is no photon in the trap. The detector will destroy any photons that enter it. It is impossible to determine if a positive result is true or false.Quantum measurements solve both of these problems. Quantum measurements preserve the photons so they can continue to measure until the end the photons natural life. False positives can be eliminated by repeating measurements. If the detector detects a photon but does not show positive, it is very likely that the subsequent measurements will show negative. Because the detector is more likely to show positive when a photon exists than when it is not (as it should), so it is unlikely that the detector will show false positives.Fermilab's expertise in creating cavities also helps prolong the lives of photons. Photons are generally lost quickly in low-quality cavities. However, photons can survive for a long period of time in Fermilabs cavities. This makes it possible to repeat measurements repeatedly.This technique, which combines expertise in quantum measurements and cavities, is 36 times more sensitive that the quantum limit. Dark photon detection might be impossible without quantum techniques.The heat is on for the search.Dark matter is a mystery that has been resolved by physicists for almost a century. The search for dark matter is progressing, however.It is exciting to see that quantum technology, including quantum measurements, quantum squeezing and quantum computing, is being used in these searches. In the search for the most mysterious particles, detection methods are still in their infancy. Scientists are developing and using the technology of tomorrow to find invisible particles.Dark matter already has a rich and long history. This could be a topic that you spend half your life studying, from the first theories to the decades-long list of failed experiments. Scientists are not afraid to add chapters or even ten that may be more interesting than the ones before. Maybe cutting-edge quantum technology will finally solve the mystery.Rhea Moutafis wrote this article and it was first published on Towards Data Science. It can be found here.
