MSGID: 1:317/3 64b0cfad   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Controlling signal routing in quantum information processing    
      
     Date:   
         July 13, 2023   
     Source:   
         University of Vienna   
     Summary:   
         Routing signals and isolating them against noise and   
         back-reflections are essential in many practical situations in   
         classical communication as well as in quantum processing. In   
         a theory-experimental collaboration, a team has achieved   
         unidirectional transport of signals in pairs of 'one-way   
         streets'. This research opens up new possibilities for more flexible   
         signaling devices.   
      
      
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   FULL STORY   
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   Routing signals and isolating them against noise and back-reflections   
   are essential in many practical situations in classical communication as   
   well as in quantum processing. In a theory-experimental collaboration,   
   a team led by Andreas Nunnenkamp from the University of Vienna and Ewold   
   Verhagen based at the research institute AMOLF in Amsterdam has achieved   
   unidirectional transport of signals in pairs of "one-way streets." This   
   research published in Nature Physics opens up new possibilities for more   
   flexible signaling devices.   
      
   Devices that allow to route signals, for example carried by light or   
   sound waves, are essential in many practical situations. This is, for   
   instance, the case in quantum information processing, where the states   
   of the quantum computer have to be amplified to read them out -- without   
   noise from the amplification process corrupting them. That is why devices   
   that allow signals to travel in a one-way channel e.g. isolators or   
   circulators are much sought- after. However, at present such devices are   
   lossy, bulky, and require large magnetic fields that break time-reversal   
   symmetry to achieve unidirectional behaviour. These limitations have   
   prompted strong efforts to find alternatives that take less space and   
   that do not rely on magnetic fields.   
      
   The new study published in Nature Physicsintroduces a new class of   
   systems characterized by a phenomenon the authors call "quadrature   
   nonreciprocity."  Quadrature nonreciprocity exploits interference between   
   two distinct physical processes. Each of the processes produces a wave   
   that contributes to the transmitted signal. Like water waves produced   
   by two thrown pebbles, the two waves can either cancel or amplify each   
   other, in a phenomenon known as interference.   
      
   This allows for unidirectional transmission of signals without   
   time-reversal breaking and leads to a distinctive dependence on   
   the phase, i.e., the quadrature, of the signal. "In these devices,   
   transmission depends not only on the direction of the signal, but also   
   on the signal quadrature" says Clara Wanjura, the theoretical lead   
   author of the study. "This realizes a 'dual carriageway' for signals:   
   one quadrature is transmitted in one direction and the other quadrature   
   in the opposite direction. Time-reversal symmetry then enforces that   
   the quadratures always travel pairwise along opposite directions in two   
   separate lanes."  The experimental team at AMOLF has demonstrated this   
   phenomenon experimentally in a nanomechanical system where interactions   
   among mechanical vibrations of small silicon strings are orchestrated by   
   laser light. Laser light exerts forces on the strings, thereby mediating   
   interactions between their different vibration 'tones'. Jesse Slim,   
   the experimental lead author of the study says: "We have developed   
   a versatile experimental toolbox that allowed us to control the two   
   different types of interactions that are needed to implement quadrature   
   nonreciprocity. This way we could reveal the resulting unidirectional   
   transport of the signals experimentally."  The work opens up new   
   possibilities for signal routing and quantum-limited amplification,   
   with potential applications in quantum information processing and sensing.   
      
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   Them Story Source: Materials provided by University_of_Vienna. Note:   
   Content may be edited for style and length.   
      
      
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   Journal Reference:   
      1. Clara C. Wanjura, Jesse J. Slim, Javier del Pino, Matteo Brunelli,   
      Ewold   
         Verhagen, Andreas Nunnenkamp. Quadrature nonreciprocity in bosonic   
         networks without breaking time-reversal symmetry. Nature Physics,   
         2023; DOI: 10.1038/s41567-023-02128-x   
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   Link to news story:   
   https://www.sciencedaily.com/releases/2023/07/230713141937.htm   
      
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