Quantum computing has emerged as one of the most promising and disruptive technologies of the 21st century. By tapping into the strange, counterintuitive world of quantum mechanics, quantum computers are poised to drastically transform our notions of computing speed and power as compared to so-called “classical” computers.

The most highly-anticipated milestone in quantum computing is the achievement of “quantum advantage” – demonstrating definitively that quantum computers can outperform the world’s best conventional computers in real-world applications. It would validate decades of scientific research seeking to build practical quantum computers.

So what exactly constitutes a quantum advantage? Why is it important? And are we any closer to reaching this goal? Let’s explore what this concept means and its significance for the computing world of tomorrow.

## Defining Quantum Advantage

The key metric that the quantum computing field uses to specify quantum advantage is speed. More specifically, showing that a quantum computer or algorithm can solve a useful, real-world problem faster than the speediest classical supercomputer utilizing the best-known solution.

For quantum computers, speed comes from their ability to exploit uniquely quantum effects like superposition and entanglement. This allows them to process an enormous number of simultaneous calculations in parallel. Classical computers, relying on transistors and binary bits, cannot replicate this massive parallelism. While current quantum computers have limits in scale, they are already demonstrating huge leaps over classical systems for specialized tasks.

If reaching quantum advantage proves consistent for certain types of complex computing problems, it could revolutionize everything from AI to drug development, financial modeling, cybersecurity, and more. There would be an enormous first-mover advantage to organizations and governments harnessing quantum computing within the next decade. The race is on!

## The Quest to Beat Classical Computers

Progress toward quantum advantage is benchmarked against a metric called computational supremacy. This signifies the threshold where a quantum processor could complete a computational task so intractable that it is essentially impossible for any existing or foreseeable classical computer.

While quantum processors have made great leaps in computational supremacy in recent years – including IBM’s 127 qubit Eagle processor in 2021 – near-unanimous scientific consensus holds that we have yet to definitively reach quantum advantage for useful real-world problems. Thus far, quantum processors and algorithms that showcase incredible computational speedups have done so using narrowly constructed test problems without practical applications.

### Google’s 2019 Claim of Quantum Supremacy

The biggest claim toward quantum advantage so far has come from Google and their 2019 test of a 53-qubit quantum computer, named Sycamore, against the world’s fastest supercomputer. They constructed a random number generation task tailored for quantum computers expected to take a state-of-the-art supercomputer 10,000 years to solve. In their Nature paper, Google reported that Sycamore solved it in just over 3 minutes.

While a remarkable feat, the computational problem itself had no real-world uses outside of demonstrating Sycamore’s capabilities. Thus, most experts did not accept it as definitive proof of useful quantum advantage. However, it brought widespread attention and excitement around just how powerful quantum computers may eventually become. With continued exponential growth forecasted for quantum computing hardware, useful quantum advantage could emerge earlier than most had predicted. Read more here.

## When Will Real Quantum Advantage Come?

While exciting progress is accelerating, nearly all experts caution that useful quantum advantage is still years away at least. A 2020 U.S. National Academy Report predicted quantum advantage is at minimum 5 to 10 years off, barring any unforeseen breakthroughs. The primary challenges remain scaling up quantum computers while limiting noise errors and decoherence of their fragile quantum states required for processing information.

One milestone to watch as an indicator is quantum processors reaching roughly 500 high-quality qubits with sufficient connectivity between them. This emerging “noisy intermediate-scale quantum” (NISQ) era of machines could be the bridge to practically realizing quantum advantage as researchers actively find ways to maximize these systems’ capabilities. Algorithms tailored specifically for NISQ processors may unlock quantum advantages earlier than brute force methods alone.

Realistically, while point benchmarks of quantum advantage are almost certain to be reached in the next several years, true quantum advantage for useful, widespread applications remains a longer-term pursuit. Still, hitting that first goalpost of conclusively beating classical computers at any real-world task will provide a major shot in the arm to quantum computing interest and funding – ushering in an era where quantum and classical machines inevitably must coexist. For scientists and companies at the cutting edge though, that quantum future has already arrived. The quantum race is on!