In a landmark achievement for quantum computing, researchers from the University of Southern California and Johns Hopkins University have demonstrated what many consider the holy grail of the field: an unconditional exponential quantum speedup.
The team, led by Professor Daniel Lidar, holder of the Viterbi Professorship in Engineering at USC, utilized two of IBM's 127-qubit Eagle quantum processors to solve a variation of Simon's problem—a mathematical challenge considered the precursor to Shor's factoring algorithm. Their results were published in Physical Review X on June 5, 2025.
"The performance separation cannot be reversed because the exponential speedup we've demonstrated is, for the first time, unconditional," explains Lidar. What makes this speedup "unconditional" is that it doesn't rely on any unproven assumptions about classical algorithms, unlike previous quantum advantage claims.
To achieve this breakthrough, the researchers implemented sophisticated error mitigation techniques, including dynamical decoupling and measurement error mitigation. These methods helped maintain quantum coherence and improve result accuracy despite the inherent noise in current quantum hardware.
The exponential speedup means the performance gap between quantum and classical approaches roughly doubles with each additional variable in the problem. As quantum processors continue to improve in quality and scale, this advantage will only grow more pronounced.
While Lidar cautions that "this result doesn't have practical applications beyond winning guessing games," the demonstration proves that quantum computers can definitively outperform classical ones for certain tasks. This validation of quantum computing's theoretical promise opens the door to practical applications that were previously only theoretical, potentially revolutionizing fields from cryptography to materials science.
IBM's 127-qubit Eagle processor, first introduced in 2021, represents a critical milestone in quantum hardware development. It was the first quantum processor to break the 100-qubit barrier, entering territory where quantum states cannot be reliably simulated on classical computers.