Quantum technology researchers at Chalmers University of Technology have successfully developed a technique to control the quantum states of light in a three-dimensional cavity. In addition to creating previously known states, the researchers also demonstrated the long-sought cubic phase state for the first time. The breakthrough is an important step toward efficient error correction for quantum computers. “We’ve shown that our technology is on par with the best in the world,” said Simone Gasparinetti, head of the experimental quantum physics research group at Chalmers and one of the study’s senior authors. ) Say.
Just as traditional computers are based on bits that can take on the value 0 or 1, the most common ways to build quantum computers use a similar approach. Quantum mechanical systems with two distinct quantum states, called quantum bits (qubits), are used as building blocks. One quantum state is assigned a value of 0, and the other is assigned a value of 1. However, thanks to the quantum mechanical states of superposition, qubits can take on states 0 and 1 at the same time, allowing quantum computers the possibility of processing large amounts of data to solve problems that cannot be solved by today’s supercomputers.
First-ever cubic phase state
A major obstacle to realizing practical quantum computers is that the quantum systems used to encode information are susceptible to noise and interference, which can lead to errors. Correcting these errors is a key challenge in the development of quantum computers. One promising approach is to replace qubits with resonators—quantum systems that have not only two defined states, but a very large number of states. These states can be likened to a guitar string, which can vibrate in many different ways. The method, called continuous-variable quantum computing, can encode the values 1 and 0 in the resonator’s multiple quantum mechanical states.
However, controlling the state of the resonator is a challenge that quantum researchers worldwide are grappling with. Chalmers’ results provide one way. The technique developed by Chalmers enables researchers to generate almost all previously demonstrated quantum states of light, such as Schrödinger’s cat or Gottesman-Kitaev-Preskill (GKP) states, as well as the cubic phase, a type of quantum state previously described only in theory status.
“The cubic phase state is something that many quantum researchers have been trying to create in practice for two decades. The fact that we have now managed to do this for the first time is a testament to how well our technique works, but the most important advance is that there are With so many states of varying complexity, we found one that could create any of them,” said Marina Kudla, a doctoral student in the Department of Microtechnology and Nanoscience and lead author of the study.
Increase door speed
The resonator is a three-dimensional superconducting cavity made of aluminum. A complex superposition of photons trapped within the resonator is created through interaction with a secondary superconducting circuit. The quantum mechanical properties of photons are controlled by applying a set of electromagnetic pulses called gates. The researchers first successfully used an algorithm to optimize a specific sequence of simple displacement gates and complex SNAP gates to generate the states of photons. When complex gates proved too long, the researchers found a way to make them even shorter, using optimal control methods to optimize electromagnetic pulses.
“The dramatic increase in the speed of our SNAP gates allows us to mitigate the effects of decoherence in quantum controllers, taking this technology one step further. We have shown that we can fully control our quantum mechanical system,” Simone Gasparinetti said.
Or, more poetically:
“I captured the light where it flourished and shaped it into some really beautiful forms,” says Marina Kudra.
Achieving this result also depends on the high quality of the physical system (the aluminum resonator itself and the superconducting circuit). Marina Kudra has previously shown how to create an aluminium cavity by first milling it and then making it very clean by heating it to 500 degrees Celsius and washing it with acid and solvent. The electronics that apply the electromagnetic gate to the cavity were developed in cooperation with the Swedish company Intermodulation Products.
The research component of the WACQT research programme
The research was carried out in Chalmers within the framework of the Wallenberg Centre for Quantum Technology (WACQT), a comprehensive research programme aimed at making Sweden a research and industry leader in quantum technology. The initiative, led by Professor Per Delsing, has the main goal of developing quantum computers.
“At Chalmers, we have the complete stack for building quantum computers, from theory to experiment, all under one roof. Solving the challenge of error correction is a major bottleneck in the development of large quantum computers, and our results are a testament to our cultural and The way it works,” Per Delsing said.
Article “Robust Preparation of Wigner-Negative States with Optimized SNAP Displacement Sequences” published in the journal PRX Quantum by Marina Kudra, Mikael Kervinen, Ingrid Strandberg, Shahnawaz Ahmed, Marco Scigliuzzo, Amr Osman, Daniel Pérez Lozano, Mats O. Tholén, Riccardo Borgani, David B. Haviland, Giulia Ferrini, Jonas Bylander, Anton Frisk Kockum, Fernando Quijandría, Per Delsing and Simone Gasparinetti.