Where We Are Today: The NISQ Era

Physicist John Preskill coined a term for our current situation: NISQ (Noisy Intermediate-Scale Quantum).

• Noisy: We don't have enough error correction yet. The qubits are "dirty."
• Intermediate-Scale: We have 50 to 1,000 qubits. Not enough to break codes, but too many to simulate with a laptop.

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1. The Three Main Gaps

To reach "Universal Fault-Tolerant Quantum Computing" (the dream), we have to bridge three gaps:

1. The Qubit Gap: We need millions of qubits. We have hundreds.
2. The Fidelity Gap: Current gates are ~99% accurate. We need them to be ~99.99% accurate to make error correction efficient.
3. The Interconnect Gap: How do you connect a thousand cryostats together? We don't have a "Quantum Internet" to link these frozen machines yet.

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2. What NISQ Can Do

Don't let the "limitations" fool you. NISQ computers are already useful for:

• Quantum Chemistry: Simulating how small atoms bond. (Classical computers struggle with even 10 electrons).
• Optimization: Finding "good enough" solutions for logistics or portfolio balancing.
• Sampling: Generating truly random patterns that are impossible for classical machines to fake.

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3. The "Hardware Frontier" Table

Decade	Stage	Key Capability
2010s	Proof of Concept	Single qubits, control logic.
2020s	NISQ Era	50-1000 noisy qubits. Cloud access.
2030s	Logical Qubit Era	Early error correction. Real drug discovery.
2040s+	Scaling Era	Millions of qubits. RSA encryption breaks.

graph TD
    A[Today: NISQ] -- Scaling & Fidelity --> B[Logical Qubits]
    B -- Networking & Integration --> C[Universal Quantum Computer]
    
    subgraph Use_Cases
    D[Chemistry]
    E[Optimization]
    F[Shor/Codebreaking]
    end
    
    A -.-> D
    A -.-> E
    B --> F

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4. Summary: The Wright Brothers Phase

We are currently in the "Kitty Hawk" phase of quantum computing. We have proven that the machine can "fly" for a few seconds. Now, we just need to figure out how to build a 747.

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Exercise: The "Resolution" Comparison

1. Think of a Digital Camera.
2. A 1990s camera (0.1 Megapixels) could take a blurry photo of a tree. You can tell it's a tree, but you can't see the leaves.
3. Today's camera (50 Megapixels) sees every detail.
4. NISQ is the 0.1 Megapixel camera. It’s "Real" photography, but we’re still waiting for the High Definition era.

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What's Next?

We’ve explored the Hardware and the Noise. But how do you actually talk to these things? In the next module, we look at the Quantum Software Stack—the languages of the future.