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   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    New quantum sensing technique reveals magnetic connections    
    Innovation combines computational and signal processing    
      
     Date:   
         February 17, 2023   
     Source:   
         DOE/Argonne National Laboratory   
     Summary:   
         A research team demonstrates a new way to use quantum sensors to   
         tease out relationships between microscopic magnetic fields.   
      
      
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   FULL STORY   
   ==========================================================================   
   A research team supported by the Q-NEXT quantum research center   
   demonstrates a new way to use quantum sensors to tease out relationships   
   between microscopic magnetic fields.   
      
      
   ==========================================================================   
   Say you notice a sudden drop in temperature on both your patio and kitchen   
   thermometers. At first, you think it's because of a cold snap, so you   
   crank up the heat in your home. Then you realize that while the outside   
   has indeed become colder, inside, someone left the refrigerator door open.   
      
   Initially, you thought the temperature drops were correlated. Later,   
   you saw that they weren't.   
      
   Recognizing when readings are correlated is important not only for your   
   home heating bill but for all of science. It's especially challenging   
   when measuring properties of atoms.   
      
   Now scientists have developed a method, reported in Science, that enables   
   them to see whether magnetic fields detected by a pair of atom-scale   
   quantum sensors are correlated or not.   
      
   "As far as I know, this is something people hadn't tried to do, and that's   
   why we see these correlations where nobody else was able to. You really   
   win from that." -- Shimon Kolkowitz, University of Wisconsin-Madison The   
   research was supported in part by Q-NEXT, a U.S. Department of Energy   
   (DOE) National Quantum Information Science Research Center led by DOE's   
   Argonne National Laboratory.   
      
   The ability to distinguish between standalone and correlated environments   
   at the atomic scale could have enormous impacts in medicine, navigation   
   and discovery science.   
      
   What happened A team of scientists at Princeton University and the   
   University of Wisconsin- Madison developed and demonstrated a new   
   technique for teasing out whether magnetic fields picked up by multiple   
   quantum sensors are correlated with each other or independent.   
      
   The team focused on a type of diamond-based sensor called a   
   nitrogen-vacancy center, or NV center, which consists of a nitrogen   
   atom next to an atom-sized hole in the crystal of carbon atoms that make   
   up diamond.   
      
   Typically, scientists measure the magnetic field strength at a single   
   NV center by averaging multiple readings. Or they might take an average   
   reading of many NV centers at once.   
      
   While helpful, average values provide only so much information. Knowing   
   that the average temperature in Wisconsin will be 42 degrees Fahrenheit   
   tomorrow tells you little about how much colder it will be at night or   
   in the northern part of the state.   
      
   "If you want to learn not just the value of the magnetic field at one   
   location or at one point in time, but whether there's a relationship   
   between the magnetic field at one location and the magnetic field at   
   another nearby - - there wasn't really a good way to do that with these   
   NV centers," said paper co-author Shimon Kolkowitz, associate professor   
   at the University of Wisconsin- Madison and Q-NEXT collaborator.   
      
   The team's new method uses multiple simultaneous readings of two NV   
   centers.   
      
   Using sophisticated computation and signal-processing techniques, they   
   obtained information about the relationship between the magnetic fields   
   at both points and could say whether the two readings resulted from the   
   same source.   
      
   "Were they seeing the same magnetic field? Were they seeing a different   
   magnetic field? That's what we can get from these measurements,"   
   Kolkowitz said. ?"It's useful information that no one had access to   
   before. We can tell the difference between the global field that both   
   sensors were seeing and those that were local."  Why it matters Quantum   
   sensors harness the quantum properties of atoms or atom-like systems   
   to pick up tiny signals -- such as the magnetic fields arising from the   
   motion of single electrons. These fields are puny: 100,000 times weaker   
   than that of a fridge magnet. Only ultrasensitive tools such as quantum   
   sensors can make measurements at nature's smallest scales.   
      
   Quantum sensors are expected to be powerful. NV centers, for example,   
   can distinguish features separated by a mere one ten thousandth of   
   the width of a human hair. With that kind of hyperzoom capability, NV   
   centers could be placed in living cells for an inside, up-close look at   
   how they function. Scientists could even use them to pinpoint the causes   
   of disease.   
      
   "What make NVs special is their spatial resolution," Kolkowitz   
   said. ?"That's useful for imaging the magnetic fields from an exotic   
   material or seeing the structure of individual proteins."  With the   
   Kolkowitz team's new method for sensing magnetic field strengths at   
   multiple points simultaneously, scientists could one day be able to map   
   atom- level changes in magnetism through time and space.   
      
   How it works How did the team make these informative measurements? They   
   got granular.   
      
   Rather than average over many raw values to arrive at the overall magnetic   
   field strength, the researchers kept track of individual readings at each   
   NV center, and then applied a mathematical maneuver called ?"covariance"   
   to the two lists.   
      
   Comparing the covariance-calculated figures -- which capture more detail   
   than a couple of raw averages -- let them see whether the fields were   
   correlated.   
      
   "We're doing that averaging differently than what's been done in the past,   
   so we don't lose this information in the process of averaging," Kolkowitz   
   said ?"That's part of what's special here."  So why hasn't covariance   
   magnetometry, as the method is called, been tested before now?  For one,   
   the team had to build an experimental setup for taking simultaneous   
   measurements at multiple NV centers. This microscope was built by the team   
   at Princeton, led by Professor Nathalie de Leon, a member of the Co-Design   
   Center for Quantum Advantage, another DOE National Quantum Information   
   Science Research Center, led by Brookhaven National Laboratory.   
      
   For another, covariance magnetometry works only when the individual   
   measurements of these tiny magnetic fields are highly reliable. (A   
   readout is only as good as its contributing measurements.) That's why the   
   researchers used a special technique called spin-to-charge conversion,   
   which produces a raw reading with more information about the magnetic   
   field for each measurement than other commonly used tools.   
      
   With spin-to-charge conversion, individual measurements take   
   longer. That's the price scientists pay for higher reliability.   
      
   However, when combined with covariance to measure minuscule, correlated   
   magnetic fields, it saves buckets of time.   
      
   "Using the conventional method, you'd have to average for 10 full days   
   continuously to get one piece of data to say that you saw this correlated   
   nanotesla signal," Kolkowitz said. ?"Whereas with this new method, it's an   
   hour or two."  By integrating covariance information with spin-to-charge   
   conversion, researchers can gain access to atomic and subatomic details   
   they didn't have before, supercharging the already powerful capabilities   
   of quantum sensing.   
      
   "As far as I know, this is something people hadn't tried to do, and   
   that's why we see these correlations where nobody else was able to,"   
   Kolkowitz said. ?"You really win from that."  This work was supported by   
   the DOE Office of Science National Quantum Information Science Research   
   Centers as part of the Q-NEXT center, the National Science Foundation,   
   the Princeton Catalysis Initiative, the DOE, Office of Science, Office   
   of Basic Energy Sciences, a Princeton Quantum Initiative Postdoctoral   
   Fellowship, and the Intelligence Community Postdoctoral Research   
   Fellowship Program by the Oak Ridge Institute for Science and Education   
   through an interagency agreement between the U.S. Department of Energy   
   and the Office of the Director of National Intelligence.   
      
       * RELATED_TOPICS   
             o Matter_&_Energy   
                   # Physics # Spintronics # Quantum_Computing #   
                   Quantum_Physics   
             o Computers_&_Math   
                   # Spintronics_Research # Quantum_Computers #   
                   Computers_and_Internet # Encryption   
       * RELATED_TERMS   
             o John_von_Neumann o Radiant_energy o Magnetic_resonance_imaging   
             o Quantum_number o Nanoparticle o Quantum_entanglement o   
             Quantum_mechanics o Quantum_computer   
      
   ==========================================================================   
   Story Source: Materials provided by   
   DOE/Argonne_National_Laboratory. Original written by Leah Hesla. Note:   
   Content may be edited for style and length.   
      
      
   ==========================================================================   
   Journal Reference:   
      1. Jared Rovny, Zhiyang Yuan, Mattias Fitzpatrick, Ahmed I. Abdalla,   
      Laura   
         Futamura, Carter Fox, Matthew Carl Cambria, Shimon Kolkowitz,   
         Nathalie P.   
      
         de Leon. Nanoscale covariance magnetometry with diamond quantum   
         sensors.   
      
         Science, 2022; 378 (6626): 1301 DOI: 10.1126/science.ade9858   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2023/02/230217081325.htm   
      
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