Andrew Côté
Andrew Côté
@Andercot
Mar 15 1 month ago 31 tweets Read on X

Quantum Computing can revolutionize our ability to simulate the natural world

Yet a lot of QC experts have given up and moved to other industries, believing a useful QC platform won't be here until <2040.

Can QC be saved this decade? Yes.

Here’s my contrarian QC thread 🧵

Tweet image 1

Quantum mechanics dominates the world of the very small, but determines properties we measure macroscopically. Nowhere is this more important than materials science.

Yet simulating crystal formation is a profoundly difficult task for classical computing. Why is it so difficult?

Tweet image 1

To accurately predict material properties we must understand that crystal structure depends on the electronic orbitals of individual atoms.

Predicting orbitals interactions means solving the Many-Body Schrodinger Equation, an impossible task for classical computing

Tweet image 1

The advantage of QC is that computing hardware naturally embodies the quantum dynamics governing electron orbital interactions. There is a direct mapping between the simulation to be solved and the simulator itself.

Explore many possible solutions concurrently

Tweet image 1

The issue with QC currently is that we haven’t learned to fully control for noise that creeps into the system. Classical computing averages thermal fluctuations out by having computing elements much larger than these fluctuations.

QC elements are necessarily small and so necessarily sensitive

Tweet image 1

This is where the pessimism about QC comes in: building a Fault Tolerant Error Corrected QC will take millions of qubits. Google recently wowed us with their Willow chip that has 100 qubits.

To go from 50 to 100 qubits took 5 years. We need a million,

Tweet image 1

The reality is that progress in the number of usable physical qubits is painstakingly slow, forever pushing forward in time the point where quantum computers have supremacy over classical for certain problems.

Many have left QC for other computing fields or quantum sensing

Tweet image 1

The question is, can quantum supremacy be accelerated faster than the pace of hardware development increases the number of usable qubits?

The answer is yes, if we understand how noise affects quantum gate operations

Tweet image 1

Single qubit gates like X,Y,Z rotations are the least noisy because only one qubit is being manipulated. Error rates are ~ 0.1%.

Two qubit gates like CNOT or SWAP have error rates 5-10 times higher

Three qubit gates are so noisy they're swappd out for sets of smaller gates

Tweet image 1

There is a vast number of ways of implementing a given functional circuit with a specific set of quantum gates, that trade-off against required depth of circuit and gate properties.

These trade-offs also depend on which QC hardware modality you're running on, and theres several

Tweet image 1

Superconducting, neutral atom, and trapped ion are the most popular approaches. Neutral atom and trapped ion devices are more stable and coherent for longer, and the qubits have better connectivity making them suitable for simulation problems with longer range interactions.

Tweet image 1

In contrast superconducting qubits have more cross-talk between elements but operate faster and are easier to scale up, making them better suited for the high volume workloads in quantum machine learning. Shallow algorithms executing very quickly.

Tweet image 1

There’s more than just those approaches however, each with a specific set of trade-offs that can make that approach competitive for a specific class of application or problem to be solved.

Tweet image 1

Balancing hardware trade-offs, gate construction, error mitigation and executing algorithms to minimize noise is extremely non-trivial.

But the win is huge: accelerating usable QC from decades to just years away

Turns out there's a company doing exactly this:

Tweet image 1

By optimizing construction and connectivity of specific quantum gates, and executing them in an approximate way that is inherently resilient to noise, can increase the depth - or longest sequence of gate elements - by up to 100x

Tweet image 1

Haiqu does for Quantum Processing Units (QPUs) what CUDA programming did for GPUs - creates a standard interface that is hardware agnostic, so engineers can use the latest hardware without worrying about implementation and execution details.

And then there’s the noise…

Tweet image 1

The resulting performance improvement is profound;

Increasing the depth of an executable circuit means we don’t have to wait decades to use QC to simulate the natural world.

Now, there's two main types of simulation:

Tweet image 1

End-to-End circuits involve many sequential gate operations where the gate operations don't change as the simulation runs.

Since noise accumulates across gate operations these are especially susceptible to decoherence, when noise swamps the solution and results are useless

Tweet image 1

Optimizing the execution means limiting the effects of noise that creep into the computation process by methods like re-designing the circuit, replacing or combining gates, or performing measurements in a subspace that is noise resilient

Tweet image 1

This last method is known as constructing a decoherence free subspace: choosing a set of basis vectors that will transform normally under quantum operations yet are resilient to the noise that accumulates through operations, increasing stability

Tweet image 1

Increasing the depth of an End-to-End circuit brings QC methods into the realm of usability for simulations like Computational Fluid Dynamics and Spectroscopy by modeling non-linear many-body interactions as they evolve through time, mapping these to quantum dynamics

Tweet image 1

The other class of methods that can greatly improve with their software layer is Variational Quantum Computing, integral to Quantum Machine Learning and where the real magic begins in unlocking materials science:

Tweet image 1

QVC uses a hybrid of QC and classical computing to evolve parameters governing quantum gates as the sim runs. Just like normal ML, QML optimizes a solution under a loss function, for QC the energy of the system

QM systems want to naturally evolve to find the lowest energy state

Tweet image 1

This makes QML the ideal method for simulating quantum chemistry experiments, like finding the lowest energy configuration of a crystal lattice, and therefore the ability to design revolutionary new materials from first principles.

What are the issues?

Tweet image 1

QVC methods don’t require the depth of End-to-End circuits but do need to execute many times on shallow circuits, meaning noise still creeps in and affects the fidelity of the simulation over time.

Tweet image 1

Noise produces 'barren plateaus,' regions where the gradient appears to vanish and the solution can no longer converge.

Tweet image 1

solves this via the combination of especially light-weight error mitigation and noise-resilient trainability techniques that make QML possible at scale. This reduces the ‘barren plateaus’ or vanishing gradients that plague QVC ML methods to reach convergence faster

Tweet image 1

An issue common to all QC applications is data loading, since the representation of the data on the circuit is susceptible to noise. Haiqu recently demonstrated an efficient and scalable data loading method with HSBC, loading the largest financial dataset to-date on IBM QPUs

Tweet image 1

Taken together Haiqu’s techniques for enhancing execution on the QPU bring applications into the realm of usability on current noisy-intermediate quantum computing devices, a decade or more ahead of fully corrected fault tolerant QC.

What’s the net-net for users?

Tweet image 1

The goal with Haiqu is to take care of all the complexities and trade-offs inherent in translating a simulation goal to an implementable quantum circuit and executing it, continuously incorporating algorithms and hardware improvements and bringing them to end-level users

Tweet image 1

This goes far beyond just noise-mitigation and smart execution strategies: it’s the entire stack between “I want to simulate something” and having that simulation run in a performance-optimized manner on available QC hardware.

Missing some Tweet in this thread? You can try to Update

More Threads by @Andercot

3 tweets • 29 days ago
Read Thread
1 tweets • 1 month ago
Read Thread
31 tweets • 1 month ago
Read Thread
17 tweets • 1 month ago
Read Thread
9 tweets • 2 months ago
Read Thread

Unroll Another Thread

Convert any Twitter threads to an easy-to-read article instantly

Have you tried our Twitter bot?

You can now unroll any thread without leaving Twitter/X. Here's how to use our Twitter bot to do it.

  • Give us a follow on Twitter. follow us
  • Drop a comment, mentioning us @unrollnow on the thread you want to Unroll.
  • Wait For Some Time, We will reply to your comment with Unroll Link.
UnrollNow Twitter Bot
Modal Image
0:00 / 0:00