Benjamin Brubaker, Postdoctoral Fellow in Quantum Physics, College of Colorado Boulder
Practically a century after dark matter was first proposed to clarify the movement of galaxy clusters, physicists nonetheless don’t know what it’s manufactured from.
Researchers world wide have constructed dozens of detectors in hopes of discovering darkish matter. As a graduate pupil, I helped design and operate one in every of these detectors, aptly named HAYSTAC. However regardless of a long time of experimental effort, scientists have but to establish the darkish matter particle.
Now, the seek for darkish matter has obtained an unlikely help from know-how utilized in quantum computing analysis. In a new paper printed within the journal Nature, my colleagues on the HAYSTAC group and I describe how we used a little bit of quantum trickery to double the speed at which our detector can seek for darkish matter. Our outcome provides a much-needed velocity enhance to the hunt for this mysterious particle.
Scanning for a darkish matter sign
There may be compelling evidence from astrophysics and cosmology that an unknown substance known as darkish matter constitutes greater than 80% of the matter within the universe. Theoretical physicists have proposed dozens of new fundamental particles that would clarify darkish matter. However to find out which – if any – of those theories is right, researchers must construct completely different detectors to check every one.
One distinguished concept proposes that darkish matter is manufactured from as-yet hypothetical particles known as axions that collectively behave like an invisible wave oscillating at a really particular frequency via the cosmos. Axion detectors – together with HAYSTAC – work one thing like radio receivers, however as a substitute of changing radio waves to sound waves, they purpose to transform axion waves into electromagnetic waves. Particularly, axion detectors measure two portions known as electromagnetic field quadratures. These quadratures are two distinct sorts of oscillation within the electromagnetic wave that will be produced if axions exist.
The primary problem within the seek for axions is that no one is aware of the frequency of the hypothetical axion wave. Think about you’re in an unfamiliar metropolis looking for a selected radio station by working your manner via the FM band one frequency at a time. Axion hunters do a lot the identical factor: They tune their detectors over a variety of frequencies in discrete steps. Every step can cowl solely a really small vary of doable axion frequencies. This small vary is the bandwidth of the detector.
Tuning a radio usually includes pausing for a number of seconds at every step to see in case you’ve discovered the station you’re searching for. That’s more durable if the sign is weak and there’s numerous static. An axion sign – in even essentially the most delicate detectors – can be terribly faint in contrast with static from random electromagnetic fluctuations, which physicists name noise. The extra noise there may be, the longer the detector should sit at every tuning step to pay attention for an axion sign.
Sadly, researchers can’t rely on choosing up the axion broadcast after a number of dozen turns of the radio dial. An FM radio tunes from solely 88 to 108 megahertz (one megahertz is a million hertz). The axion frequency, in contrast, could also be anyplace between 300 hertz and 300 billion hertz. On the charge today’s detectors are going, discovering the axion or proving that it doesn’t exist may take more than 10,000 years.
Squeezing the quantum noise
On the HAYSTAC group, we don’t have that form of endurance. So in 2012 we got down to velocity up the axion search by doing every little thing doable to scale back noise. However by 2017 we discovered ourselves working up towards a fundamental minimum noise limit due to a regulation of quantum physics often called the uncertainty principle.
The uncertainty precept states that it’s not possible to know the precise values of sure bodily portions concurrently – for example, you may’t know each the place and the momentum of a particle on the identical time. Recall that axion detectors seek for the axion by measuring two quadratures – these particular sorts of electromagnetic discipline oscillations. The uncertainty precept prohibits exact data of each quadratures by including a minimal quantity of noise to the quadrature oscillations.
In standard axion detectors, the quantum noise from the uncertainty precept obscures each quadratures equally. This noise can’t be eradicated, however with the suitable instruments it may be managed. Our group labored out a technique to shuffle across the quantum noise within the HAYSTAC detector, lowering its impact on one quadrature whereas rising its impact on the opposite. This noise manipulation method is named quantum squeezing.
In an effort led by graduate college students Kelly Backes and Dan Palken, the HAYSTAC group took on the problem of implementing squeezing in our detector, utilizing superconducting circuit know-how borrowed from quantum computing analysis. Basic-purpose quantum computer systems stay a long way off, however our new paper exhibits that this squeezing know-how can instantly velocity up the seek for darkish matter.
Greater bandwidth, quicker search
Our group succeeded in squeezing the noise within the HAYSTAC detector. However how did we use this to hurry up the axion search?
Quantum squeezing doesn’t cut back the noise uniformly throughout the axion detector bandwidth. As a substitute, it has the largest effect at the edges. Think about you tune your radio to 88.three megahertz, however the station you need is definitely at 88.1. With quantum squeezing, you’ll have the ability to hear your favourite music taking part in one station away.
On the earth of radio broadcasting this could be a recipe for catastrophe, as a result of completely different stations would intrude with each other. However with just one darkish matter sign to search for, a wider bandwidth permits physicists to look quicker by masking extra frequencies without delay. In our newest outcome we used squeezing to double the bandwidth of HAYSTAC, permitting us to seek for axions twice as quick as we may earlier than.
Quantum squeezing alone isn’t sufficient to scan via each doable axion frequency in an inexpensive time. However doubling the scan charge is a giant step in the suitable route, and we consider additional enhancements to our quantum squeezing system might allow us to scan 10 occasions quicker.
No one is aware of whether or not axions exist or whether or not they are going to resolve the thriller of darkish matter; however because of this surprising utility of quantum know-how, we’re one step nearer to answering these questions.
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