IonQ and Duke report on the advancement of the multiqubit gate for quantum computing

Researchers from Duke University and IonQ reported today that they have developed a powerful new approach to running multi-qubit entanglement gates that “can dramatically simplify quantum circuit structures, speed up their execution, and extend the power of quantum computing systems facing decoherence”.

IonQ maintains that the technique, at least at present, can only be run on its quantum platform. “[N]o Other available quantum computing architectures, not even other ion-based quantum computers, can use this new family of N-qubit gates,” according to Christopher Monroe, co-founder and chief scientist at IonQ.

Effective implementation of entangled multi-qubit gates has long been difficult. Most systems can do two-qubit gates, and even those aren’t easy. Entanglement, of course, is one of the two key attributes that give quantum computing its powerful advantage over classical computing. Usually tangle it connects qubits in such a way that when the entangled state of one qubit is altered, all the others instantly know about it and also change their state (true parallelism). This is the spooky action-at-a-distance phenomenon that no one understands but is consistently confirmed by experiment. (Overlap is the other distinguishing attribute of quantum computing.)

Schematic of the trapped ion quantum processor. Credit: IonQ

ingeniously developed algorithms, by Shor The algorithm is one example, it can take advantage of the entanglement and superstition features of quantum computers to perform select calculations faster and tackle other calculations that are impractical on classical computers.

IonQ/Duke’s progress is significant and its paper (N-body interactions between trapped ion qubits through spin-dependent compression) was published today on arXiv.org. The introduction to the document sums up the challenge very well:

“The core ingredient of a quantum computer is controllable quantum entanglement of its degrees of freedom, which allows the system to evolve in an exponentially large state space that can encode certain otherwise intractable problems. The qubit-and-gate model of a quantum computer employs a universal set of operations, such as rotations of a single qubit and NOT gates controlled by two qubits.

“While these few-qubit interactions are sufficient for general computation and can be used to build many-body entangled states, many-qubit interactions can dramatically simplify quantum circuit structures, speed up their execution, and extend the power of systems. quantum computer scientists facing decoherence For example, direct N-qubit operations such as the N-qubit Toffoli gate are expected to find native use in quantum adders and multipliers, Grover lookups, error-correcting coding, quantum algorithms variations to calculate electronic properties of molecules and materials, and simulations. of nuclear structure and lattice gauge theories”.

As the researchers explained, the central idea behind trapped-ion quantum gates is the coupling between spins and motion (phonons) through spin-dependent forces. “Due to the Coulomb interaction between the trapped ions, their motion around equilibrium can be expressed by collective normal modes of harmonic oscillation. We focus on coupling through a single phonon mode via a near-resonant driving force, although the generalization to multiple modes is straightforward. (A figure from the document with an overview is shown below – it’s a bit long but worth scanning – click to enlarge.)

The new quantum gate, the researchers report, is a novel way to operate on many connected qubits at once and takes advantage of the multi-qubit communication bus available only at IonQ and the Duke Quantum Center (DQC) computers. “The new family of gates includes the Toffoli N-qubit gate, which inverts a selected qubit if and only if all other qubits are in a particular state. Unlike standard two-qubit quantum computing gates, the N-qubit Toffoli gate acts on many qubits at once, leading to more efficient operations. The gate appears naturally in many common quantum algorithms,” said IonQ.

There are many underlying qubit technologies in various stages of development. Trapped ion systems have force coherence, but are sometimes criticized for being difficult to scale.

IonQ says its quantum computers uniquely feature full connectivity and a wide communication bus that allows all qubits to talk to each other simultaneously. It is noteworthy that IonQ was the first of the first pure quantum companies. make public what he did last fall using a SPAC approach. Rigetti, which is betting on a different underlying qubit technology, semiconductor-based superconducting qubits, has announced plans to go public through SPAC and this week D-Wave announced similar plans.

The pressure on the new public and soon-to-be-public quantum computing companies will no doubt increase to show results. IBM has said that 2023 is the year it will bring a broader quantum advantage to market.

Side view of assembled IonQ trap

In today’s announcement, IonQ said: “This discovery follows a series of announcements about IonQ’s research efforts and scaling preparations. In December, IonQ announced that plans to use barium ions as qubits in their systems, spawning a wave of advantages that they believe will enable advanced quantum computing architectures. Last year, the team also debuted in the industry first. reconfigurable and evaporated multicore quantum architecture glass trap technologyof which are expected to contribute to scaling the number of qubits in IonQ’s quantum computers.”

The company says this new work can lead to significant efficiency gains in solving fundamental quantum algorithms, such as Grover’s search algorithm, variational quantum eigensolvers (VQE), and arithmetic operations such as addition and multiplication. “These use cases are ubiquitous in quantum computing applications and are central to IonQ’s work in quantum chemistry, quantum finance, and quantum machine learning. They are also key components of the commonly accepted industry benchmarks for quantum computers,” IonQ reported.

As always, it’s best to read the most recent article directly for a fuller understanding.

link to paper, https://arxiv.org/abs/2202.04230

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