Building quantum computers just got easier with new technique

Researchers have devised a new method of building quantum computers, creating and “annihilating” qubits on demand, using a femtosecond laser to dope silicon with hydrogen.

This breakthrough could pave the way for quantum computers that use programmable optical qubits or “spin-photon qubits” to connect quantum nodes across a remote network.

In turn, this creates a quantum internet that is more secure and capable of transmitting more data than current optical-fiber information technologies.

The research team, led by Lawrence Berkeley National Laboratory (Berkeley Lab), is the first to use this technique, which could enable the quantum computing industry to overcome challenges in qubit fabrication and quality control.

Importance of qubit connection in quantum computers

Quantum computers have the potential to solve complex problems in human health, drug discovery, and artificial intelligence millions of times faster than some of the world’s fastest supercomputers.

A network of quantum computers could advance these discoveries even faster. However, before that can happen, the computer industry will need a reliable way to string together billions of qubits — or quantum bits — with atomic precision.

Connecting qubits has been a challenge for the research community. Some methods form qubits by placing an entire silicon wafer in a rapid annealing oven at very high temperatures, resulting in qubits randomly forming from defects in silicon’s crystal lattice.

Without knowing exactly where qubits are located in a material, a quantum computer of connected qubits will be difficult to realize.

Precision qubit formation with lasers

The new method uses a gas environment to form programmable defects called “color centers” in silicon. These color centers are candidates for special telecommunications qubits or “spin photon qubits.”

The method also uses an ultrafast femtosecond laser to anneal silicon with pinpoint precision where those qubits should precisely form.

As Kaushalya Jhuria is a postdoctoral scholar in Berkeley Lab’s Accelerator Technology & Applied Physics (ATAP) Division and first author on the study.

She explains, “To make a scalable quantum architecture or network, we need qubits that can reliably form on-demand, at desired locations, so that we know where the qubit is located in a material. And that’s why our approach is critical.”

Once it’s known where a specific qubit is sitting, scientists can determine how to connect this qubit with other components in the system and make a quantum network.

Ci Center: Rising star in quantum computers

During their experiments, the researchers uncovered a quantum emitter called the Ci center. Due to its simple structure, stability at room temperature, and promising spin properties, the Ci center is an interesting spin photon qubit candidate that emits photons in the telecom band.

“We knew from the literature that Ci can be formed in silicon, but we didn’t expect to actually make this new spin photon qubit candidate with our approach,” Jhuria said.

The researchers learned that processing silicon with a low femtosecond laser intensity in the presence of hydrogen helped to create the Ci color centers.

Further experiments showed that increasing the laser intensity can increase the mobility of hydrogen, which passivates undesirable color centers without damaging the silicon lattice.

Future of quantum computers

The team plans to use the technique to integrate optical qubits in quantum devices such as reflective cavities and waveguides, and to discover new spin photon qubit candidates with properties optimized for selected applications.

“Now that we can reliably make color centers, we want to get different qubits to talk to each other – which is an embodiment of quantum entanglement – and see which ones perform the best. This is just the beginning,” said Jhuria.

As Cameron Geddes, Director of the ATAP Division, states, “The ability to form qubits at programmable locations in a material like silicon that is available at scale is an exciting step towards practical quantum networking and computing.”

Berkeley Lab’s breakthrough in qubit control

In summary, the research conducted by the Berkeley Lab team opens up exciting new possibilities for the future of quantum computing and networking.

By developing a method to create and control qubits with precision using femtosecond lasers and hydrogen doping, they have taken a significant step towards overcoming the challenges that have hindered the development of scalable quantum systems.

As the team continues to explore the potential of the Ci center and other spin photon qubit candidates, they bring us closer to realizing the full potential of quantum technology.

Their work lays the foundation for the creation of secure, high-capacity quantum networks and computers that could revolutionize fields ranging from healthcare and drug discovery to artificial intelligence and beyond.

The full study was published in the journal Nature Communications.

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