MSGID: 1:317/3 63edb16e   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Engineers discover a new way to control atomic nuclei as 'qubits'    
    Using lasers, researchers can directly control a property of nuclei   
   called spin, that can encode quantum information.    
      
     Date:   
         February 15, 2023   
     Source:   
         Massachusetts Institute of Technology   
     Summary:   
         Researchers propose a new approach to making qubits, the basic   
         units in quantum computing, and controlling them to read and write   
         data. The method is based on measuring and controlling the spins   
         of atomic nuclei, using beams of light from two lasers of slightly   
         different colors.   
      
      
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   FULL STORY   
   ==========================================================================   
   In principle, quantum-based devices such as computers and sensors could   
   vastly outperform conventional digital technologies for carrying out   
   many complex tasks. But developing such devices in practice has been a   
   challenging problem despite great investments by tech companies as well   
   as academic and government labs.   
      
      
   ==========================================================================   
   Today's biggest quantum computers still only have a few hundred "qubits,"   
   the quantum equivalents of digital bits.   
      
   Now, researchers at MIT have proposed a new approach to making qubits   
   and controlling them to read and write data. The method, which is   
   theoretical at this stage, is based on measuring and controlling the   
   spins of atomic nuclei, using beams of light from two lasers of slightly   
   different colors. The findings are described in a paper published in the   
   journal Physical Review X, written by MIT doctoral student Haowei Xu,   
   professors Ju Li and Paola Cappellaro, and four others.   
      
   Nuclear spins have long been recognized as potential building blocks   
   for quantum-based information processing and communications systems,   
   and so have photons, the elementary particles that are discreet packets,   
   or "quanta," of electromagnetic radiation. But coaxing these two quantum   
   objects to work together was difficult because atomic nuclei and photons   
   barely interact, and their natural frequencies differ by six to nine   
   orders of magnitude.   
      
   In the new process developed by the MIT team, the difference in the   
   frequency of an incoming laser beam matches the transition frequencies   
   of the nuclear spin, nudging the nuclear spin to flip a certain way.   
      
   "We have found a novel, powerful way to interface nuclear spins with   
   optical photons from lasers," says Cappellaro, a professor of nuclear   
   science and engineering. "This novel coupling mechanism enables their   
   control and measurement, which now makes using nuclear spins as qubits   
   a much more promising endeavor."  The process is completely tunable,   
   the researchers say. For example, one of the lasers could be tuned to   
   match the frequencies of existing telecom systems, thus turning the   
   nuclear spins into quantum repeaters to enable long-distance- quantum   
   communication.   
      
   Previous attempts to use light to affect nuclear spins were indirect,   
   coupling instead to electron spins surrounding that nucleus, which in   
   turn would affect the nucleus though magnetic interactions. But this   
   requires the existence of nearby unpaired electron spins and leads   
   to additional noise on the nuclear spins. For the new approach, the   
   researchers took advantage of the fact that many nuclei have an electric   
   quadrupole, which leads to an electric nuclear quadrupolar interaction   
   with the environment. This interaction can be affected by light in order   
   to change the state of the nucleus itself.   
      
   "Nuclear spin is usually pretty weakly interacting," says Li. "But by   
   using the fact that some nuclei have an electric quadrupole, we can induce   
   this second- order, nonlinear optical effect that directly couples to   
   the nuclear spin, without any intermediate electron spins. This allows   
   us to directly manipulate the nuclear spin."  Among other things, this   
   can allow the precise identification and even mapping of isotopes of   
   materials, while Raman spectroscopy, a well-established method based   
   on analogous physics, can identify the chemistry and structure of the   
   material, but not isotopes. This capability could have many applications,   
   the researchers say.   
      
   As for quantum memory, typical devices presently being used or considered   
   for quantum computing have coherence times -- meaning the amount of time   
   that stored information can be reliably kept intact -- that tend to be   
   measured in tiny fractions of a second. But with the nuclear spin system,   
   the quantum coherence times are measured in hours.   
      
   Since optical photons are used for long-distance communications through   
   fiber- optic networks, the ability to directly couple these photons to   
   quantum memory or sensing devices could provide significant benefits in   
   new communications systems, the team says. In addition, the effect could   
   be used to provide an efficient way of translating one set of wavelengths   
   to another. "We are thinking of using nuclear spins for the transduction   
   of microwave photons and optical photons," Xu says, adding that this   
   can provide greater fidelity for such translation than other methods.   
      
   So far, the work is theoretical, so the next step is to implement   
   the concept in actual laboratory devices, probably first of all in a   
   spectroscopic system.   
      
   "This may be a good candidate for the proof-of-principle experiment,"   
   Xu says.   
      
   After that, they will tackle quantum devices such as memory or   
   transduction effects, he says.   
      
   The team also included Changhao Li, Guoqing Wang, Hua Wang, Hao Tang,   
   and Ariel Barr, all at MIT.   
      
       * RELATED_TOPICS   
             o Matter_&_Energy   
                   # Spintronics # Physics # Optics # Nuclear_Energy   
             o Computers_&_Math   
                   # Spintronics_Research # Quantum_Computers #   
                   Computers_and_Internet # Encryption   
       * RELATED_TERMS   
             o Quantum_computer o Scientific_method o Quantum_entanglement   
             o Electron o Electron_configuration o Quantum_number o   
             World_Wide_Web o Trigonometry   
      
   ==========================================================================   
   Story Source: Materials provided by   
   Massachusetts_Institute_of_Technology. Original written by David   
   L. Chandler. Note: Content may be edited for style and length.   
      
      
   ==========================================================================   
   Journal Reference:   
      1. Haowei Xu, Changhao Li, Guoqing Wang, Hua Wang, Hao Tang, Ariel   
      Rebekah   
         Barr, Paola Cappellaro, Ju Li. Two-Photon Interface of Nuclear Spins   
         Based on the Optonuclear Quadrupolar Effect. Physical Review X,   
         2023; 13 (1) DOI: 10.1103/PhysRevX.13.011017   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2023/02/230215143644.htm   
      
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