Quantum Computers A Step Closer To Reality

Engineers make a significant advancement in the design of quantum computers. 

A significant roadblock to quantum computers becoming a reality has been overcome thanks to quantum engineers from UNSW Sydney. 

  • They developed a novel method that they claim would allow them to manage millions of spin qubits—the fundamental units of information in a silicon quantum processor. 
  • Until far, quantum computer engineers and scientists have only been able to demonstrate the control of a few qubits in a proof-of-concept model of quantum processors. 
  • However, the team has discovered what they call "the missing jigsaw piece" in the quantum computer design, which should allow them to manage the millions of qubits required for very complicated computations, according to their new study, which was published today in Science Advances. 
  • Dr. Jarryd Pla, a professor at UNSW's School of Electrical Engineering and Telecommunications, says his research group wanted to solve a problem that had plagued quantum computer scientists for decades: how to control millions of qubits without taking up valuable space with additional wiring, which consumes more electricity and generates more heat. 

"Controlling electron spin qubits depended on our providing microwave magnetic fields by sending a current through a wire directly near the qubit up to this point," Dr. Pla explains. 

  • "If we want to scale up to the millions of qubits that a quantum computer would require to tackle globally important issues like the creation of new vaccines, this presents some serious difficulties." 
  • To begin with, magnetic fields diminish rapidly with distance, so we can only control the qubits that are nearest to the wire. 
  • As we brought in more and more qubits, we'd need to add more and more wires, which would take up a lot of space on the chip." 
  • And, since the device must function at temperatures below -270°C, Dr. Pla claims that adding additional wires will create much too much heat in the chip, jeopardizing the qubits' stability. 
  • "With this wiring method, we're only able to manage a few qubits," Dr. Pla explains. 

A thorough rethinking of the silicon chip structure was required to solve this issue. 

  • Rather of putting thousands of control lines on a tiny silicon device with millions of qubits, the researchers investigated the possibility of using a magnetic field generated from above the chip to operate all of the qubits at the same time. 
  • The concept of controlling all qubits at the same time was originally proposed by quantum computing experts in the 1990s, but until today, no one had figured out how to accomplish it in a practical manner. 
  • "After removing the cable adjacent to the qubits, we devised a new method for delivering microwave-frequency magnetic control fields throughout the device. In theory, we could send control fields to as many as four million qubits "Dr. Pla agrees. 

A crystal prism termed a dielectric resonator was inserted immediately above the silicon chip by Dr. Pla and his colleagues. 

  • When microwaves are directed into a resonator, the wavelength of the microwaves is reduced dramatically. 
  • "Because the dielectric resonator reduces the wavelength to less than one millimeter, we now have a highly effective conversion of microwave power into the magnetic field that controls all of the qubits' spins." 

    • The first is that we don't need a lot of power to create a strong driving field for the qubits, which means we don't produce a lot of heat. 
    • The second is that the field is very consistent throughout the device, ensuring that millions of qubits have the same degree of control." Despite the fact that Dr. 

Pla and his team had created a prototype resonator technology, they lacked the silicon qubits with which to test it. 

  • So he spoke to his UNSW engineering colleague, Scientia Professor Andrew Dzurak, whose team had proven the earliest and most precise quantum logic utilizing the same silicon fabrication process as traditional computer chips during the previous decade. 
  • "When Jarryd presented me with his new concept, I was absolutely blown away," Prof. Dzurak recalls, "and we immediately went to work to see how we might combine it with the qubit devices that my team has created." Ensar Vahapoglu from my team and James Slack-Smith from Jarryd's were assigned to the project as two of our top Ph.D. students. 

"When the experiment turned out to be a success, we were ecstatic. This issue of controlling millions of qubits had been bothering me for a long time, since it was a significant stumbling block in the development of a full-scale quantum computer." 

  • Quantum computers with thousands of qubits to address business issues, which were once just a pipe dream in the 1980s, may now be less than a decade away. 
  • In addition, due of their capacity to simulate very complex systems, they are anticipated to offer fresh firepower to addressing global problems and creating new technologies. 

Quantum computing technology has the potential to help climate change, medicine and vaccine development, code decryption, and artificial intelligence. 

  • The team's next goal is to utilize this new technique to make designing near-term silicon quantum computers easier. 
  • "The on-chip control wire is removed, making room for more qubits and the rest of the components needed to create a quantum processor. 
  • It simplifies the job of moving on to the next stage of manufacturing devices with tens of qubits "Prof. Dzurak agrees. 
  • "While there are still technical hurdles to overcome before computers with a million qubits can be built," Dr. Pla adds, "we are thrilled that we now have a method to manage them."

~ Jai Krishna Ponnappan

You may also want to read more about Quantum Computing here.

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