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17/09/20/028248 story

IBM Simulates Beryllium Hydride Molecule Using a Quantum Computer

posted by martyb on Wednesday September 20 2017, @09:20AM   
from the big-deal-about-very-small-things dept.

takyon writes:

https://www.hpcwire.com/2017/09/14/ibm-breaks-ground-complex-quantum-chemistry/

IBM [reported] in Nature Communications the use of a novel algorithm to simulate BeH₂ (beryllium-hydride) on a quantum computer. This is the largest molecule so far simulated on a quantum computer. The technique, which used six qubits of a seven-qubit system, is an important step forward and may suggest an approach to simulating ever larger molecules.

"Instead of forcing previously known classical computing methods onto quantum hardware, the scientists reversed the approach by building an algorithm suited to the capability of the current available quantum devices. This allows for extracting the maximal quantum computational power to solve problems that grow exponentially more difficult for classical computers," according to the IBM announcement.

[...] Today, simulating even small molecules with the needed accuracy to predict energy states and reactivity is hard. IBM performed the numerical simulation on H₂, LiH, and BeH₂. "While this model of BeH₂ can be simulated on a classical computer, IBM's approach has the potential to scale towards investigating larger molecules that would traditionally be seen to be beyond the scope of classical computational methods, as more powerful quantum systems get built," noted IBM.

Beryllium hydride

Hardware-efficient variational quantum eigensolver for small molecules and quantum magnets (DOI: 10.1038/nature23879) (DX)

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Original Submission

• Comment Below Threshold

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• only six qubits (Score: 1) by khallow on Thursday September 21 2017, @08:14AM

  by khallow (3766) on Thursday September 21 2017, @08:14AM (#571055) Journal

  What's remarkable is that they claim to be able to get useful information about simulations of these molecules from only six qubits and sequences of pairwise entangling operations. It appears that the approach is to decompose the position-momentum state of the hydrogen atoms into a few orthogonal shells around the central beryllium atom (see figure 1 in article), labeled by 1s, 1s', 2s, and 2p (see here for an example [wikipedia.org] using electrons - doesn't have the 1s' configuration with electrons) and fermion-style up and down spin (represented by up and down arrows in figure 1). Symmetries then eliminate the 1s' configurations from needing to be considered as part of the computation resulting in six qubits in total. They've then come up with approximations to the interactions between the shells using pairwise entangling operations on the qubits.
  
  One of the researchers claims that they'll eventually be able to model potential pharmaceutical molecules very accurately. I'm a bit skeptical. Those are much larger with much more complex interactions (particularly, if they're modeling one complex molecule acting on another complex molecule). While the number of qubits may be manageable, the interactions between the qubits might not. A rapidly growing number of pairwise entangling operations might be required.