Researchers face major hurdle in quantum computing

In a series of treatises, the Rochester researchers report significant advances in improving the transfer of information in quantum systems.

Quantum science has the potential to revolutionize modern technology with more efficient computers, communications, and sensing devices. However, achieving these technical goals remains a challenge, especially with regard to the efficient transfer of information in quantum systems.

A typical computer is made up of billions of transistors called bits. Quantum computers, on the other hand, are based on qubits (also called qubits) which can be created from a single electron.

Unlike ordinary transistors, which are either “0” (off) or “1” (on), qubits can be both “0” and “1”. The ability of individual qubits to occupy these so-called superposition states is underpinned by the great potential of quantum computers, as they are in multiple states at the same time. However, like ordinary computers, quantum computers require a way to transfer quantum information between distant qubits, posing a major experimental challenge.

A quantum processor semiconductor chip connected to a printed circuit board is shown. Credit: University of Rochester Photo / J. Adam Fenster

In a series of treatises published in Nature CommunicationResearchers from the University of Rochester, including John Nicole, assistant professor of physics and astronomy, and graduate students Yadav Kandel and Heifen Chao, who are the main authors of the treatise, Quantum computing By improving the transfer of information between electrons in a quantum system.

Using the new route

In a treaty[1] For the first time, researchers have demonstrated a way of transferring information between quantum bits using electron spin qubits, called adiabatic quantum state transfer (AQT). Unlike most methods of transferring information between qubits that rely on carefully tuned electric or magnetic field pulses, AQT is immune to pulse errors and noise.

To imagine how AQT works, imagine you are driving your car and want to park. If you don’t brake at the right time, your car won’t move the way you want it to, which can be detrimental. In this sense, the control pulses (accelerator and brake pedals) sent to the car must be carefully adjusted. The AQT doesn’t matter how long or how hard you press the pedal. In other words, the car always goes to the right place. As a result, AQT has the potential to improve the transfer of information between qubits, which is essential for quantum networks and error correction.

Researchers have demonstrated the effectiveness of AQT using entanglement. Entanglement is one of the basic concepts of quantum physics in which the properties of one particle affect the properties of another, even when the particles are far apart from each other. Using AQT, the researchers were able to transfer the quantum spin state of an electron through a chain of four electrons in a semiconductor quantum dot. It is a very small nanometric semiconductor with amazing properties. It is the longest chain of spin states ever transferred and is linked to records set by researchers. Before Nature paper..

“This demonstration is an important step in quantum computing with spin qubits, because AQT is robust against pulse errors and noise and has potential for major applications in quantum computing.” Nichol said.

Take advantage of the strange state of matter

In another treaty[2] The researchers demonstrated another method of transferring information between qubits using a substance in an exotic state called a time crystal. A temporal crystal is a strange state of matter in which the interactions between the particles that make up a crystal indefinitely stabilize the vibration of the system. Imagine a clock that goes on and on. The pendulum of a clock vibrates over time, like a vibrating time crystal.

By applying a series of electric field pulses to the electrons, the researchers were able to create a state that resembled a time crystal. They discovered that this state could be used to enhance the spin-state motion of electrons in a series of semiconductor quantum dots.

“Our research is the first step in showing that materials in strange and exotic states, such as time crystals, have the potential to be used in quantum information processing applications such as the transfer of information between qubits. ” Nicole said. “Theoretically, this scenario also shows how we can implement other single and multiple qubit operations that can be used to improve the performance of quantum computers.”

AQT and Time Crystal are both different, but they can be used with quantum computing systems to improve performance.

“These two results show a strange and interesting way in which quantum physics can send information from one place to another. He is building a viable quantum computer and network. It was one of the main challenges at the time, ”explains Nicole.

The references:

  1. Yadav P. Kandel, Haifeng Qiao, Saeed Fallahi, Geoffrey C. Gardner, Michael J. Manfra, John M. Nichol, Adiabatic Quantum State Transition in Semiconductor Quantum Dot Spin Chain, April 12, 2021 Nature Communication..
    DOI: 10.1038 / s41467-021-22416-5
  2. “Floquet Enhanced Spin Trading”, Haifeng Qiao, Yadav P. Kandel, John S. Van Dyke, Saed Fallahi, Geoffrey C. Gardner, Michael J. Manfra, Edwin Barnes, John M. Nichol, April 6, 2021 Nature Communication..
    DOI: 10.1038 / s41467-021-22415-6

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