Google realizes quantum chemical simulation, the world’s first case so far

Naija Tech News (NTN) on 30, and in content, Google realizes quantum chemical simulation, the world’s first case so far, chemical, Google, quantum, simulation .

Quantum computing has discovered a new world!

On August 27th, the Google quantum computing research team announced that it has made breakthroughs in modeling chemical reaction paths using quantum computers. This is the first and largest chemical quantum computing to date.

His published paper entitled “Hartree-Fock on a Superconducting Qubit Quantum Computer” (Hartree-Fock on a Superconducting Qubit Quantum Computer), appeared on the cover of “Science” magazine on the same day.

Quantum computing simulates chemical reactions

It is worth mentioning that this is the second time Google has appeared on the cover of “Science” magazine due to quantum research.

The first time was in October last year when Google released the results of quantum superiority research. In this paper, Google achieved quantum superiority with an array of 54 qubits, and completed the prescribed operation within 200 seconds. The same operation also took 10,000 years on the world’s largest supercomputing summit at the time. carry out.

It can be said that this research will have epoch-making significance in the history of quantum computing.

The Sycamore processor that played a key role in this research is also the processor used in the quantum computer in this chemical experiment.

Sycamore processor

The reason why quantum computer simulation is adopted is that atoms and molecules are controlled by a quantum mechanical system and can store information and perform calculations through qubits, so it is expected to become the best method for accurate simulation.

Specifically, the researchers used the noise robust variable quantum feature solving algorithm VQE (variational quantum eigensolver) to directly simulate the chemical mechanism.

In the reaction, two nitrogen atoms and two hydrogen atoms form a diazene molecule. The process is that hydrogen atoms continuously move around nitrogen atoms to form different structures. After testing, it is found that the results of the quantum simulation and the simulation performed on the traditional computer are basically consistent, and the effectiveness of the quantum simulation can be determined.

In addition, the entire Hartree-Fock equation is similar to a real chemical system, which is twice the traditional chemical calculation on a quantum computer and contains ten times the quantum gate operation.

Although the nitrogen-hydrogen reaction is a relatively basic chemical reaction, the results can be easily obtained without even being equipped with a quantum computer to simulate, but the researcher Babbush said that this study verified that the algorithm developed by the current quantum computer can achieve the required experimental prediction Accuracy opens up a path to realistic simulation of quantum chemical systems.

Next, they will expand the quantum simulation algorithm to the chemical reactions of more complex and larger molecules , and this will be very easy, only requiring more qubits and smaller algorithm adjustments. He emphasized that

In the future, we can even use quantum simulation to develop new chemical substances .

VQE algorithm reduces quantum errors

There are many ways to use quantum computers to simulate the ground state energy of molecular systems. In this study, researchers focused on quantum algorithm “building blocks” or circuit element diagrams, and improved their performance through VQE.

In the traditional setting, the circuit element diagram is equivalent to the Hartree-Fock model, which is an important circuit component of the optimized chemical simulation algorithm. The robust error suppression of this component is essential for accurate simulation.

Errors in quantum computing are caused by the interaction between quantum circuits and the environment (even small temperature differences may cause qubit errors).

Regardless of the errors caused by qubits or other aspects, when simulating chemical reactions, quantum algorithms must solve these errors at a lower cost. It is like implementing a quantum error correction code.

The most popular way to resolve errors is to use VQE. In the experiment, the researchers chose VQE, which was developed a few years ago. It treats the quantum processor as a neural network, which can optimize the parameters of the quantum circuit by minimizing the cost function and solve the noisy quantum logic.

In short, just as traditional neural networks can tolerate defects in data through optimization, VQE can dynamically adjust quantum circuit parameters to resolve errors in quantum computing.

Sycamore processor achieves high precision

As mentioned above, the quantum computer used in this study uses the Sycamore processor.

This chemical simulation experiment requires fewer qubits, but requires higher fidelity of quantum gates to solve the chemical bond problem. This has led to the development of new, targeted calibration techniques that can best amplify errors and facilitate their diagnosis and correction.

Simulate Hartree-Fock’s energy prediction of molecular geometry on 10 qubits

The error may originate in the quantum hardware stack.

Sycamore has 54 bits and is composed of more than 140 individually adjustable components, each of which is controlled by high-speed analog electrical pulses. To achieve precise control of the entire equipment, more than 2,000 control parameters need to be fine-tuned, and even small errors in these parameters can quickly expand the error in the total calculation.

In order to accurately control the equipment, the researchers used an automated framework that maps the control problem onto a graph with thousands of nodes, each of which represents a physical experiment to determine an unknown parameter. Traversing this graph can be transferred from the prior knowledge of the device to the high-fidelity quantum processor, and can be completed in less than a day.

Ultimately, these techniques, along with algorithm error mitigation techniques, reduce errors by orders of magnitude. As shown below:

The above figure shows that the energy of the linear chain of hydrogen atoms increases as the bond distance between each atom increases. Among them, the solid line is a Hartree-Fock simulation using a classic computer, and the point is calculated using a Sycamore processor.

The figure above shows the two accuracy measures (distortion and mean absolute error) for each point calculated using Sycamore. “Raw” is the original error from Sycamore. “+PS” is an error from the number of correction electrons. “+Puriflication” is a measure to alleviate errors in the correct state. “+VQE” is the optimized result after eliminating all errors.

Open the blueprint for chemical calculation

Google CEO Sundar Pichai (Sundar Pichai) expressed his joy on Twitter for the first time. He said,

This latest achievement in the field of quantum chemistry is the largest chemical quantum calculation to date, and it is also the first time that a quantum computer is used to model chemical reaction paths.

The quantum calculation of electronic energy can break the curse of dimensionality that plagues multi-particle quantum mechanics. In other words, general-purpose quantum computers have the potential to fundamentally change computational chemistry and material science. However, in these fields, the strong electronic correlation is very important for traditional electronics. The structural approach brought obstacles.

This study uses Sycamore processors, VQE models, and error mitigation strategies to open up a new path for quantum chemical systems. Through the simulation test of up to 12 qubits, the accuracy of the chemical reaction is ensured, and the possibility of expansion to larger and more complex chemical systems is provided.

The research team said that this experiment can become a blueprint for quantum processors to realize chemical calculations and a starting point for the advantages of physical simulation. More importantly, it is known in the future how to modify the quantum circuits used in this experiment in a simple way so that they are no longer effectively simulatable, which will set new directions for improved quantum algorithms and applications.

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