When a molecule absorbs light, it undergoes a whirlwind of quantum-mechanical transformations. Electrons jump between energy levels, atoms vibrate, and chemical bonds shift—all within millionths of a billionth of a second.
These processes underpin everything from photosynthesis in plants and DNA damage from sunlight, to the operation of solar cells and light-powered cancer therapies.
Yet despite their importance, chemical processes driven by light are difficult to simulate accurately. Traditional computers struggle, because it takes vast computational power to simulate this quantum behavior.
On the other hand, quantum computers are themselves quantum systems—thus, they exhibit quantum behavior inherently. Consequently, this makes them ideal choices for modeling chemical processes.
Until now, quantum devices have only been able to calculate unchanging things, such as the energies of molecules.
Our study
, published in the
Journal of the American Chemical Society
, demonstrates we can also model how those molecules change over time.
We experimentally simulated how specific real molecules behave after absorbing light.
Simulating reality with a single ion
We used what is called a trapped-ion quantum computer. This works by manipulating individual atoms in a vacuum chamber, held in place with electromagnetic fields.
Typically, quantum computers use quantum bits, known as qubits, for storing data. Nonetheless, to emulate the actions of molecules, we additionally employed atomic vibrations within the computer referred to as “bosonic modes.”
This technique is called mixed qudit-boson simulation. It dramatically reduces how big a quantum computer you need to simulate a molecule.
We mimicked the behavior of three molecules when they absorb light: allene, butatriene, and pyrazine. These molecules each exhibit intricate electronic and vibrational dynamics following light absorption, rendering them perfect subjects for testing.
Our simulation, utilizing a laser and a solitary atom within the quantum computer, decelerated these processes by a staggering factor of 100 billion. While actual interactions occur in femtoseconds, our simulated version unfolded over milliseconds—slowing things down sufficiently for clear observation.
A millionfold more efficient
What makes our experiment particularly significant is the size of the quantum computer we used.
Performing the same simulation with a traditional quantum computer (without using bosonic modes) would require 11 qubits, and to carry out roughly 300,000 “entangling” operations without errors. This is well beyond the reach of current technology.
By contrast, our approach accomplished the task by zapping a single trapped ion with a single laser pulse. We estimate our method is at least a million times more resource-efficient than standard quantum approaches.
We similarly modeled “open-system” behavior, wherein the molecule engages with its surroundings. This kind of simulation generally poses a more significant challenge for classical computing systems.
Through introducing regulated noise into the ion’s surroundings, we mimicked how actual molecules shed energy. This demonstrated that environmental intricacy can likewise be encompassed by quantum simulation.
What’s next?
This work is an important step forward for quantum chemistry. Even though current quantum computers are still limited in scale, our methods show that small, well-designed experiments can already tackle problems of real scientific interest.
Simulating the real-world behavior of atoms and molecules is a key goal of quantum chemistry. It will make it easier to understand the properties of different materials, and may accelerate breakthroughs in medicine, materials and energy.
We believe that with a modest increase in scale—to perhaps 20 or 30 ions—quantum simulations could tackle chemical systems too complex for any classical supercomputer. That would open the door to rapid advances in drug development, clean energy, and our fundamental understanding of chemical processes that drive life itself.
This article is republished from
The Conversation
under a Creative Commons license. Read the
original article
.
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