The readout signal is enhanced by 10,000 times, and the silicon carbide qubit makes a breakthrough
In the field of quantum computing, researchers are still grappling with how to easily read the information held in qubits, as well as increase the time quantum information is held (the qubit's coherence time), which is typically limited to microseconds or milliseconds.
A team of researchers at the U.S. Department of Energy's Argonne National Laboratory and the University of Chicago achieved two major breakthroughs to overcome these common challenges for quantum systems. They were able to read out their qubits on demand and then remain fully quantum for more than 5 seconds -- a new record for this type of device. In addition, the researchers' qubits are made of an easy-to-use material called silicon carbide, which is widely found in light bulbs, electric vehicles and high-voltage electronics.
"Conservation of quantum information on human timescales is uncommon," said David Awschalom, senior scientist at Argonne National Laboratory, director of the Q-NEXT Center for Quantum Research, Liew Family Professor of Molecular Engineering and Physics at the University of Chicago, and principal investigator on the project. , five seconds is enough to send a light-speed signal to the moon and back. Even after nearly 40 orbits around Earth, this light will still correctly reflect the qubit state -- paving the way for the creation of a distributed quantum internet."
By creating a system of qubits that can be fabricated in ordinary electronic devices, the researchers hope to open up a new avenue for quantum innovation using a technique that is both scalable and cost-effective.
"This basically brings silicon carbide to the forefront of quantum communication platforms," said University of Chicago graduate student Elena Glen, one of the paper's first authors. "It's exciting because it's easy to scale up because we already know how Use this material to make useful devices."
The findings were published in the February 2 issue of the journal Science Advances [1].
The chips used in the experiments were made of silicon carbide, an inexpensive and commonly used material.
10,000 times stronger signal
The researchers' first breakthrough was to make silicon carbide qubits easier to read.
Every computer needs a way to read information encoded into bits. For semiconductor qubits, as with the team's qubits, the typical readout method is to address the qubit with a laser and measure the light that is emitted back. However, this process is challenging because it requires very efficient detection of single photons.
In this work, the researchers used carefully designed laser pulses to add an electron to a qubit based on its initial quantum state (0 or 1). The qubits are then read out using a laser -- the same way as before.
Control and readout of quantum states.
"The light emitted now reflects the presence or absence of electrons, and the signal is 10,000 times larger," Glen said. By converting fragile quantum states into stable electron charges, we can measure these states very easily. With this signal enhancement, every time we check what state a qubit is in, we can get a reliable answer. This measurement is called a 'single readout', and with it, we can unlock many useful quantum technologies ."
With a single readout approach, scientists can focus on making their quantum states as durable as possible -- a serious challenge for quantum technology, where qubits can easily lose information due to noise in their environment.
The researchers grew high-purity samples of silicon carbide, reducing background noise that interferes with the function of the qubits. Then, by applying a series of microwave pulses to the qubits, they extended the time the qubits hold quantum information, known as "coherence."
"These pulses decouple the qubit from noise sources and errors by rapidly flipping the quantum state," said Chris Anderson of the University of Chicago, one of the paper's first authors. "Each pulse is like pressing the undo button on our qubit, Any errors that may occur between erase pulses."
The researchers believe that longer coherence times are possible. Extending the coherence time could have major implications, such as how complex operations a future quantum computer can handle, or how small a signal can be detected by a quantum sensor.
"For example, this new record time means we can perform more than 100 million quantum operations before our quantum state is perturbed," Anderson said.
The highest measured coherence time is 5.3±1.3 seconds, which is two orders of magnitude better than previous systems of this type.
The scientists also see multiple potential applications for the technology they developed. "The ability to perform a single readout opens up a new opportunity to use the light emitted by silicon carbide qubits to help develop the quantum internet of the future," said Glen. "In a fundamental operation like quantum entanglement, the state of a qubit can be read by The state of another qubit is known, which has been achieved in a silicon carbide system."
"We basically made a converter that translates quantum states into the realm of electrons, which is the language of classical electronics, like what's in your smartphone," Anderson said. "We want to create a new generation that is sensitive to single electrons. A device that can also accommodate quantum states. Silicon carbide can do both, and that's why we think it's really promising."
Reference link:
[1] https://www.science.org/doi/10.1126/sciadv.abm5912
[2] https://phys.org/news/2022-02-quantum-states-seconds.html
