Researchers have used quantum superposition to help qubits violate a fundamental quantum limit, allowing them to maintain information five times longer. This breakthrough involves a three-qubit system that demonstrates extreme correlations over time. The finding could enhance quantum computing and metrology applications.
Physicists have long debated the boundary between quantum and classical worlds, with a key test developed by Anthony Leggett and Anupam Garg in 1985 to assess quantum behavior through temporal correlations. These correlations measure how strongly an object's properties at different times relate, with quantum objects showing unusually high scores. However, scores were believed capped by the temporal Tsirelson’s bound (TTB), a limit even quantum systems could not exceed.
A team led by Arijit Chatterjee at the Indian Institute of Science Education and Research in Pune challenged this. Using a carbon-based molecule containing three qubits—the basic units of quantum computers—they configured the system to surpass the TTB dramatically. The first qubit controlled the second, or target, qubit via a quantum superposition state, effectively making it behave in two contradictory ways at once, such as rotating both clockwise and counterclockwise. A third qubit then measured the target's properties.
This setup produced one of the largest plausible violations of the TTB. As a result, the target qubit resisted decoherence—the loss of quantum information over time—five times longer than usual. Chatterjee noted that "this robustness is desirable and useful in any situation where qubits must be precisely controlled, such as for computation."
Team member H. S. Karthik from the University of Gdansk in Poland highlighted applications in quantum metrology, saying there are "procedures... that could be enhanced by this kind of qubit control," like precise sensing of electromagnetic fields.
Le Luo from Sun Yat-Sen University in China praised the work for expanding understanding of quantum temporal behavior, as the extreme TTB violation shows profound quantumness in the system. Karthik added that it "is a strong testament to just how much quantumness there was in the whole three-qubit system."
The research appears in Physical Review Letters (DOI: 10.1103/vydp-9qqq).
