Analysts from RIKEN and QuTech a coordinated effort between TU Delft and the Netherlands Organization for Applied Scientific Research (TNO) have accomplished a vital achievement toward the improvement of an issue open minded quantum computer.
They had the option to show a two-qubit entryway loyalty of 99.5 percent higher than the close to 99% viewed as the edge for building fault-tolerant computers utilizing electron turn qubits in silicon, which are promising for huge scope quantum computers as the nanofabrication innovation for building them as of now exists.
This study was published in Nature.
The world is currently engaged in a race to develop large-scale quantum computers that could greatly outperform traditional computers in several areas.
However, a number of reasons have hampered these efforts, including the problem of decoherence, or noise generated in the qubits. As the number of qubits increases, the problem gets more acute, preventing scaling up.
It is thought that a two-qubit gate fidelity of at least 99 percent is required to implement the surface code for error correction in order to produce a large-scale computer that might be employed for practical applications.
The presented result makes spin qubits, for the first time, competitive against superconducting circuits and ion traps in terms of universal quantum control performance. This study demonstrates that silicon quantum computers are promising candidates, along with superconductivity and ion traps, for research and development toward the realization of large-scale quantum computers.
Seigo Tarucha
Certain types of computers have done this utilizing qubits based on superconducting circuits, trapped ions, and nitrogen-vacancy centers in diamond, but these are difficult to scale up to the millions of qubits required to perform real quantum computation with error correction.
To overcome these issues, the team opted to use a controlled-NOT (CNOT) gate to nanofabricate a quantum dot structure on a strained silicon/silicon germanium quantum well substrate.
Because of the sluggish gate speed in previous trials, the gate fidelity was limited. They meticulously constructed the device and tweaked it by applying varying voltages to the gate electrodes to improve the gate speed. This method coupled a well-known rapid single-spin rotation approach with a huge two-qubit coupling.
As a result, the gate speed was ten times faster than earlier attempts. Interestingly, they discovered that while it was previously assumed that increasing gate speed always resulted in improved fidelity, there was a point beyond which increasing the speed actually made the fidelity worse.
They discovered that a property called the Rabi frequency, which is a marker of how the qubits change states in response to an oscillating field, is critical to the system’s performance, and they discovered a frequency range for which the single-qubit gate fidelity was 99.8% and the two-qubit gate fidelity was 99.5 percent, clearing the required threshold.
They demonstrated that they could achieve universal operations, which means that they could perform all of the basic operations that make up quantum operations, such as a single qubit operation and a two-qubit operation, at gate fidelities over the error correction threshold.
The researchers used a two-qubit Deutsch-Jozsa algorithm and the Grover search technique to test the new system’s capabilities. Both algorithms provide correct results with a fidelity of 96 percent to 97 percent, proving that silicon quantum computers are capable of performing quantum calculations with great precision.
Akito Noiri, the first author of the study, says, “We are very happy to have achieved a high-fidelity universal quantum gate set, one of the key challenges for silicon quantum computers.”
Seigo Tarucha, leader of the research groups, said, “The presented result makes spin qubits, for the first time, competitive against superconducting circuits and ion traps in terms of universal quantum control performance. This study demonstrates that silicon quantum computers are promising candidates, along with superconductivity and ion traps, for research and development toward the realization of large-scale quantum computers.”
Two distinct research teams present experimental demonstrations of equally high-fidelity universal quantum gate sets achieved in silicon qubits in the same issue of Nature.
In quantum dots, a team at QuTech exploited electron spin qubits as well. As nuclear spin qubits, another team at UNSW Sydney (University of New South Wales) employed a pair of ion-implanted phosphorus nuclei in silicon.
