Taking Stock of Quantum Computers – How Many Useful Qubits Exist Today?

H Hannan

Taking Stock of Quantum Computers - How Many Useful Qubits Exist Today?
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Tracking the current state of quantum computing hardware can feel like playing an intense game of numbers. Tech giants and startups relentlessly tout qubit counts to showcase progress. But with multiple quantum technologies and metrics in flux, understanding real capabilities requires parsing the hype. How many qubits displaying potential for practical use exist today?

No universal quantum computers fulfilling the exponential promise currently operate. However, the rapid scaling of noisy intermediate-scale quantum (NISQ) devices offers hints of coming massive disruptive potential from fields like optimization and simulation in the near-term horizon.

Superconducting Circuits – The Most Mainstream Modality

Most major players like IBM, Google, and Rigetti leverage tiny superconducting circuits cooled to frigid temperatures to generate qubits. Encoding data in microwave pulses, these solid-state designs integrate readily with classical semiconductor fabrication methods, enabling intensive commercialization and research efforts.

Thousands of superconducting experimental quantum processors have been produced to date, largely accessible via cloud services. Devices range from small prototypes in academic labs to IBM’s largest 433 qubit system commercially available on the cloud. Google recently previewed a rumored million qubit computer internally after demonstrating quantum advantage on a 53 qubit photonic chip in 2019.

Trapped Ions – Leaders in Qubit Performance Benchmarks

Trapped ion approaches employ individual charged atoms held via electromagnetic fields in vacuum chambers. Laser pulses manipulate and couple the isolated atoms to enact quantum logic operations. While fiddlier to control, trapped ions achieve record coherence times exceeding seconds.

IonQ and Honeywell lead trapped ion computing efforts with IonQ holding the algorithmic qubit record – currently at 32 high-quality qubits. Honeywell plans to unveil a 10 qubit system in 2023 on approach to an ambitious 2030 goal of a 1 million+ qubit computer.

Neutral Atoms – An Emergent Quantum Medium

Neutral atom quantum computing takes advantage of quantum phenomena using atoms that have no net electric charge. It promises inherent stability by relying on fundamental atomic properties. Early players here include ColdQuanta, QuEra Computing, Pasqal, and Quantum Machines.

ColdQuanta has unveiled a 100 qubit neutral atom processor available via cloud access, with plans to hit 1,000 by 2024. Competitors suggest similar near-term qubit targets will catalyze scaling. If realized, such rapid growth keeps neutral atoms hotly competitive.

Photonic Chips – Racing to Unleash Optical Parallelism

Employing photons as qubits, photonic quantum computing generates quantum states of light manipulated with mirrors, waveguides, and beamsplitters etched onto specialized silicon or glass chips. Xanadu, PsiQuantum, and Rahko are key industry players vying to actualize ultra-scalable optical quantum computing.

Xanadu and PsiQuantum currently offer cloud access to approximately 5 qubit photonic prototypes but outline plans for 1 million+ qubit machines by around 2030. The technology’s innate fine-grained control makes enormous qubit counts feasible once engineering hurdles are solved.

Quantum Annealers – Restricted Use Cases But Real-World Deployments

While not gate-based universal quantum computers, quantum annealers built by D-Wave tackle discrete optimization problems using exotic physics phenomena. Roughly 5000 qubit versions now see niche applications in logistics, finance, healthcare, and more – some of quantum computing’s first forays into commercialization.

Quantum Volume – Measuring Broad Quantum Capabilities

With the diverse qubit modalities and counts increasing exponentially yearly, better benchmarking metrics have become essential. “Quantum volume” helps gauge both qubit numbers and gate fidelities to approximate the largest random circuit a system can successfully run. State-of-the-art quantum volume now sits around 128.

Resource Estimates for Future Universal Fault-Tolerant Quantum

When gauging quantum progress, it helps estimate the resources experts believe will eventually be necessary for broadly capable, fault-tolerant quantum computers combining error correction and fault tolerance:

  • Qubits: Likely billions to 100s of billions
  • Gates: Billions per second, with error rates of 1 in 100 million
  • Physical footprint: Entire buildings or larger

The Path to Large-Scale Quantum Computing

Building a commercially relevant fault-tolerant quantum computer remains an immense challenge still measured in years, if not decades. Myriad engineering obstacles around fragile quantum states demand breakthroughs to demonstrate unambiguous quantum advantage.

But despite hurdles, hardware iteration velocities keep increasing. With key performance metrics now doubling annually, quantum systems seem to present almost a Moore’s Law-like cadence. Further assuming merely linear future progress, system capabilities could profoundly disrupt industries in the next decade.

Leading experts estimate quantum computers may exhibit supremacy and economic impact along the following rough timeline:

2023-2025: Specialized quantum advantage that beats supercomputers
2025-2030: Broad quantum advantage across meaningful applications
2030-2040: Commercially viable fault-tolerant quantum systems

The quantum computing revolution appears closer than it may seem as quantum investment pours into the ecosystem. Savvy organizations should plan accordingly and hedge their risks. Because much like Y2K, by the time fault-tolerant quantum emerges, it may already be too late to adapt.

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