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EPFL scientists have taken inspiration from Schrödinger’s famous cat thought experiment to create an innovative and robust quantum computing system. This breakthrough, called the “critical cat code,” employs bosons to store and process information in a way that surpasses previous designs, providing enhanced reliability and error resistance.
Quantum computing harnesses the principles of quantum mechanics to encode and manipulate data, offering the potential to solve complex computational problems that are currently beyond the reach of classical computers. Unlike classical computers that utilize bits representing either 0 or 1, quantum computers utilize qubits—fundamental units of quantum information.
Professor Vincenzo Savona, director of the Center for Quantum Science and Engineering at EPFL, highlights the broad impact of quantum computing: “With applications ranging from drug discovery to optimization and simulations of complex biological systems and materials, quantum computing has the potential to reshape vast areas of science, industry, and society.”
The key difference between classical bits and qubits lies in their ability to exist in a superposition of both 0 and 1 states simultaneously. This unique characteristic enables quantum computers to explore multiple solutions concurrently, making them significantly faster for specific computational tasks. However, the delicate nature of quantum systems makes them susceptible to errors resulting from environmental interactions.
“Developing strategies to protect qubits from errors or to detect and correct them once they occur is vital for realizing large-scale, fault-tolerant quantum computers,” explains Savona. Together with EPFL physicists Luca Gravina and Fabrizio Minganti, Savona has achieved a significant breakthrough by proposing the “critical Schrödinger cat code,” which offers advanced resilience against errors. This novel encoding scheme has the potential to revolutionize the reliability of quantum computers.
So, what exactly is the “critical Schrödinger cat code”? In 1935, physicist Erwin Schrödinger presented a thought experiment challenging the prevailing Copenhagen interpretation of quantum mechanics. In Schrödinger’s experiment, a cat in a sealed box is subjected to a flask of poison and a radioactive source. If a single atom of the radioactive source decays, the Geiger counter detects the radioactivity, shattering the flask and killing the cat.
According to the Copenhagen interpretation, if the atom is initially in a superposition, the cat inherits the same state and becomes a superposition of being both alive and dead. Savona explains, “This state exactly represents the notion of a quantum bit realized at the macroscopic scale.”
Scientists have previously drawn inspiration from Schrödinger’s cat to create an encoding technique known as “Schrödinger’s cat code.” In this technique, the 0 and 1 states of the qubit are encoded onto two opposite phases of an oscillating electromagnetic field in a resonant cavity, similar to the cat’s dead or alive states.
“Schrödinger cat codes have been implemented in the past using two different approaches,” Savona clarifies. “One relies on anharmonic effects in the cavity, while the other depends on precisely engineered cavity losses. In our work, we have bridged the two approaches, operating in an intermediate regime that combines the best of both worlds. Despite being previously considered unproductive, this hybrid regime enhances error suppression capabilities.” The core idea is to operate near the critical point of a phase transition, which explains the “critical” aspect of the critical cat code.
The critical cat code brings an additional advantage: it demonstrates exceptional resistance to errors resulting from random frequency shifts. These shifts often pose significant challenges in operations involving multiple qubits. This breakthrough overcomes a major hurdle and opens the path to realizing devices with multiple interacting qubits—the fundamental requirement for building a quantum computer.
Reference: Source: EPFL (Author: Nik Papageorgiou)
