Quantum computing has advanced rapidly in recent years. As quantum systems grow in capability and application, there is a need to benchmark their performance. Quantum volume is emerging as a key metric to gauge the power of quantum computers. This article explains what quantum volume is, how it is calculated, its usefulness, and the state of quantum volume in 2024.
What is Quantum Volume?
Quantum volume is a hardware agnostic metric proposed by IBM to estimate the capability and scalability of quantum computers and quantum processing units (QPUs). It aims to measure both the number of qubits in a system as well as the degree of quantum noise. Put simply, quantum volume estimates how many good quality qubits a quantum computer has. The higher the quantum volume, the more complex problems the quantum system can solve.
Why quantum volume is useful?
Quantum volume provides a practical benchmark to track progress in quantum computing. It accounts for both qubit count and connectivity, as well as error correction. This provides a more wholistic view of system performance compared to looking at qubit count alone. It enables standardized comparison between different quantum processors that may have varying underlying technologies. This is useful for evaluating hardware from IBM, Google, Rigetti, IonQ and other players. For users, quantum volume gives guidance on the complexity of problems that could be run on a specific quantum system today.
How is quantum volume calculated?
The quantum volume is found by running random quantum circuits on the quantum processor. Circuits are chosen to use all the qubits and exercise real gate operations between arbitrary qubits. The number of qubits and circuit depth is increased until the quantum computer can no longer run the random circuits to give the right outputs. The maximum circuit depth that achieves a specified level of accuracy becomes the quantum volume. Higher quantum volume requires thicker circuits with more sequential gates between arbitrarily connected qubits. This stresses the quantum system more to reveal performance limits.
Quantum Volume Projections
|Projected QV in 2024
|Projected QV in 2027
What contributes to higher quantum volume?
Several hardware capabilities and benchmarks factor into achieving better quantum volume:
- More qubits: Having more high quality qubits to work with increases quantum volume
- Lower error rates: Reducing noise and interference inside the quantum processor
- Greater connectivity: More links enabling qubits to interact creates larger circuits
- Better controls Precision pulse sequences to manipulate quantum states
- Effective error correction: Detecting and fixing qubit errors mid-circuit
Software efficiency also plays a role in fully utilizing hardware to demonstrate its maximum volume.
The state of quantum volume in 2024
In 2024, quantum volume numbers still remain modest, but leading systems are achieving quantum volumes in the low hundreds. This is up from values below 10 just a few years ago. IBM has publicly disclosed a quantum volume of 128 with a 433 qubit processor. Rigetti and IonQ also claim to have quantum computers reaching equivalently high quantum volumes based on benchmarking.
Thanks to algorithmic improvements that make the most of limited quantum resources, commercially available systems can practically tackle data analysis problems in areas like finance, pharmaceuticals, and machine learning. However, performance remains noisy and error-prone for general applications. Wider adoption awaits quantum volumes in the thousands, anticipated later in the decade. Software stacks and developer tools are also maturing to leverage high quantum volume hardware.
The path to higher quantum volume
In the race to demonstrate practical quantum advantage and commercial viability, boosting quantum volume is a key milestone. Google, IBM, and Honeywell lead in pushing beyond 1,000 qubits in 2024. Behind them IonQ, Rigetti, and startup Pasqal are innovating ways to connect and control larger grids of qubits.
With each player having unique and proprietary technology, from superconducting qubits to trapped ions, there are parallel innovation tracks to scale up quantum volume. Investment continues pouring in from governments, corporations, and VCs to back quantum computing startups. Along with academic research, this drives rapid iteration in progress.
Will quantum volume continue as the key benchmark?
Quantum volume has gained broad acceptance since its introduction in 2019. However, as quantum systems grow extremely powerful in the coming years, quantum volume may no longer suffice to compare performance. More nuanced metrics that capture application specific performance on standardized benchmarks will gain traction. These could better quantify business value for users than abstract volume measures.
Groups like the Quantum Economic Development Consortium (QED-C) are already working to develop such practical benchmarking for evaluating quantum machines. As with classical computers, we can expect a proliferation of benchmarks targeted for applications in chemistry, optimization, machine learning, finance and other domains.
Quantum volume offers a useful shorthand today to gauge and compare the fledgling capabilities of quantum computers working to achieve practical potential. As the technology matures in power and commercial viability, we will evolve more refined performance metrics that quantify the business value quantum computers deliver on real-world problems. Quantum volume has set the ball rolling to spur the development of better benchmarks for tomorrow’s quantum enhanced applications.
What are the highest quantum volume numbers today?
In 2024, IBM and Google claim test quantum volume numbers in the low 100s. But commercially accessible quantum volume still remains below 128.
Can quantum volume compare classical computers too?
No, classical computers will score 0 on quantum volume tests which specifically benchmark quantum phenomena and properties.
What is a good quantum volume to show quantum advantage?
There is no fixed threshold, but quantum volumes above 500 are estimated to be enough to demonstrate potential practical value in areas like finance or ML.
Could better software make quantum volume go higher?
Yes, smarter compilers and error correction schemes that optimize circuit design for specific hardware can boost the effective quantum volume.
Will quantum volume keep going higher forever?
There will be physical limits to how far quantum volume can realistically scale as engineers battle quantum noise. But we are far from those limits yet today.
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