**The use of natural quantum interactions allows for faster and more robust calculations for Grover’s algorithm and many others.**

*Scientists at Los Alamos National Laboratory have developed a revolutionary method quantum computing approach that uses natural quantum interactions. This method promises long-lived qubits, efficient problem solving with Grover’s algorithm, and significant error resiliency.*

A potentially revolutionary theoretical approach to quantum computing hardware sidesteps much of the problematic complexity found in current quantum computers. The strategy implements an algorithm in natural quantum interactions to process a variety of real-world problems faster than classical computers or conventional gate-based quantum computers can.

Our discovery eliminates many demanding requirements for quantum hardware, said Nikolai Sinitsyn, a theoretical physicist at Los Alamos National Laboratory. He co-authored an article on the approach, published Aug. 14 in the journal *Physical review a*. Natural systems, such as the electronic rotations of defects in diamonds, have exactly the kind of interactions needed for our computational process.

Sinitsyn said the team hopes to work with experimental physicists also at Los Alamos to demonstrate their approach using ultracold atoms. Modern technologies in ultracold atoms are advanced enough to demonstrate such calculations with about 40 to 60 qubits, he said, which is enough to solve many problems not currently accessible with classical, or binary, computation. A qubit is the basic unit of quantum information, analogous to a bit in classical computing.

#### Longest-lived qubits

Instead of creating a complex system of logic gates between a number of qubits that must all share quantum entanglement, the new strategy uses a simple magnetic field to rotate the qubits, like the spins of electrons, in a natural system. The precise evolution of the spin states is all that is needed to implement the algorithm. Sinitsyn said the approach could be used to solve many practical problems proposed for quantum computers.

Quantum computing remains a nascent field hampered by the difficulty of connecting qubits into long strings of logic gates and maintaining the quantum entanglement required for computation. Entanglement breaks down in a process known as decoherence, as entangled qubits begin interacting with the world outside the computer’s quantum system, introducing errors. This happens quickly, limiting the calculation time. True error correction has not yet been implemented on quantum hardware.

The new approach relies on natural rather than induced entanglement, so it requires fewer connections between qubits. This reduces the impact of decoherence. Therefore, qubits live relatively long, Sinitsyn said.

#### Advances in quantum algorithms

The theory paper from the Los Alamos team showed how the approach could solve a number partitioning problem using Grover’s algorithm faster than existing quantum computers. As one of the best-known quantum algorithms, it enables unstructured searches of large datasets that eat up conventional computing resources. For example, Sinitsyn said, Grover’s algorithm can be used to evenly divide the running time of tasks between two computers, so that they finish at the same time, along with other practical work. The algorithm is particularly suited to idealized and error-correcting quantum computers, although it is difficult to implement on today’s error-prone machines.

#### Error resilience and simplicity

Quantum computers are built to perform calculations much faster than any classical device can, but until now they have been extremely difficult to make, Sinitsyn said. A conventional quantum computer implements quantum circuit sequences of elementary operations with several pairs of qubits.

Los Alamos theorists have proposed an intriguing alternative.

We have noticed that for many famous computational problems it is sufficient to have a quantum system with elementary interactions, where only a single quantum spin achievable with two qubits interacts with the rest of the computational qubits, Sinitsyn said. So a single magnetic pulse acting only on the central spin implements the most complex part of Grover’s quantum algorithm. Called Grovers’ oracle, this quantum operation indicates the desired solution.

No direct interactions between the computational qubits and no time-dependent interactions with the central spin are needed in the process, he said. Once the static couplings between the central spin and the qubits are set up, the entire computation is just applying simple time-dependent external field pulses that rotate the spins, he said.

Importantly, the team demonstrated that such operations can be done quickly. The team also found that their approach is topologically secure. That is, it is resistant to many errors in the accuracy of control fields and other physical parameters even without quantum error correction.

Reference: Topologically protected Grovers oracle for the partition problem by Nikolai A. Sinitsyn and Bin Yan, August 14, 2023, *Physical review a*.

DOI: 10.1103/PhysRevA.108.022412

Funding: Department of Energy, Office of Science, Office of Advanced Scientific Computing Research, and laboratory-led research and development program at Los Alamos National Laboratory.

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