MSGID: 1:317/3 63d89971   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    New method to control electron spin paves the way for efficient quantum   
   computers    
    The method, developed by University of Rochester scientists, overcomes   
   the limitations of electron spin resonance    
      
     Date:   
         January 30, 2023   
     Source:   
         University of Rochester   
     Summary:   
         Researchers have developed a new method for manipulating information   
         in quantum systems by controlling the spin of electrons in silicon   
         quantum dots. The results provide a promising new mechanism for   
         control of qubits, which could pave the way for the development   
         of a practical, silicon-based quantum computer.   
      
      
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   FULL STORY   
   ==========================================================================   
   Quantum science has the potential to revolutionize modern technology with   
   more efficient computers, communication, and sensing devices. Challenges   
   remain in achieving these technological goals, however, including how   
   to precisely manipulate information in quantum systems.   
      
      
   ==========================================================================   
   In a paper published in Nature Physics, a group of researchers from the   
   University of Rochester, including John Nichol, an associate professor of   
   physics, outlines a new method for controlling electron spin in silicon   
   quantum dots -- tiny, nanoscale semiconductors with remarkable properties   
   -- as a way to manipulate information in a quantum system.   
      
   "The results of the study provide a promising new mechanism for coherent   
   control of qubits based on electron spin in semiconductor quantum dots,   
   which could pave the way for the development of a practical silicon-based   
   quantum computer," Nichol says.   
      
   Using quantum dots as qubits A regular computer consists of billions   
   of transistors, called bits. Quantum computers, on the other hand,   
   are based on quantum bits, also known as qubits.   
      
   Unlike ordinary transistors, which can be either "0" (off) or "1" (on),   
   qubits are governed by the laws of quantum mechanics and can be both   
   "0" and "1" at the same time.   
      
   Scientists have long considered using silicon quantum dots as qubits;   
   controlling the spin of electrons in quantum dots would offer a way   
   to manipulate the transfer of quantum information. Every electron in a   
   quantum dot has intrinsic magnetism, like a tiny bar magnet. Scientists   
   call this "electron spin" -- the magnetic moment associated with each   
   electron -- because each electron is a negatively charged particle that   
   behaves as though it were rapidly spinning, and it is this effective   
   motion that gives rise to the magnetism.   
      
   Electron spin is a promising candidate for transferring, storing,   
   and processing information in quantum computing because it offers long   
   coherence times and high gate fidelities and is compatible with advanced   
   semiconductor manufacturing techniques. The coherence time of a qubit   
   is the time before the quantum information is lost due to interactions   
   with a noisy environment; long coherence means a longer time to perform   
   computations. High gate fidelity means that the quantum operation   
   researchers are trying to perform is performed exactly as they want.   
      
   One major challenge in using silicon quantum dots as qubits, however,   
   is controlling electron spin.   
      
   Controlling electron spin The standard method for controlling electron   
   spin is electron spin resonance (ESR), which involves applying oscillating   
   radiofrequency magnetic fields to the qubits. However, this method   
   has several limitations, including the need to generate and precisely   
   control the oscillating magnetic fields in cryogenic environments,   
   where most electron spin qubits are operated. Typically, to generate   
   oscillating magnetic fields, researchers send a current through a wire,   
   and this generates heat, which can disturb cryogenic environments.   
      
   Nichol and his colleagues outline a new method for controlling   
   electron spin in silicon quantum dots that does not rely on oscillating   
   electromagnetic fields.   
      
   The method is based on a phenomenon called "spin-valley coupling,"   
   which occurs when electrons in silicon quantum dots transition between   
   different spin and valley states. While the spin state of an electron   
   refers to its magnetic properties, the valley state refers to a different   
   property related to the electron's spatial profile.   
      
   The researchers apply a voltage pulse to harness the spin-valley   
   coupling effect and manipulate the spin and valley states, controlling   
   the electron spin.   
      
   "This method of coherent control, by spin-valley coupling, allows for   
   universal control over qubits, and can be performed without the need   
   of oscillating magnetic fields, which is a limitation of ESR," Nichol   
   says. "This allows us a new pathway for using silicon quantum dots to   
   manipulate information in quantum computers."   
       * RELATED_TOPICS   
             o Matter_&_Energy   
                   # Spintronics # Physics # Quantum_Physics #   
                   Quantum_Computing   
             o Computers_&_Math   
                   # Spintronics_Research # Quantum_Computers #   
                   Computers_and_Internet # Encryption   
       * RELATED_TERMS   
             o Quantum_entanglement o Quantum_computer o Quantum_dot   
             o Quantum_number o Silicon o Electron_configuration o   
             Quantum_tunnelling o Atomic_orbital   
      
   ==========================================================================   
   Story Source: Materials provided by University_of_Rochester. Original   
   written by Lindsey Valich. Note: Content may be edited for style and   
   length.   
      
      
   ==========================================================================   
   Journal Reference:   
      1. Xinxin Cai, Elliot J. Connors, Lisa F. Edge, John   
      M. Nichol. Coherent   
         spin-valley oscillations in silicon. Nature Physics, 2023; DOI:   
         10.1038/ s41567-022-01870-y   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2023/01/230130144803.htm   
      
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