Scalable device for quantum information processing

Researchers in NPL’s (UK National Physical Laboratory) Quantum Detection Group have demonstrated for the first time a monolithic 3DNature Nanotechnology – A monolithic array of three-dimensional ion traps fabricated with conventional semiconductor technology. The device could be used in quantum computation, where entangled qubits are used to execute powerful quantum algorithms. As an example, factorisation of large numbers by a quantum algorithm is dramatically faster than with a classical algorithm.

Scalable ion traps consisting of a 2D array of electrodes have been developed, however 3D trap geometries can provide a superior potential for confining the ions. Creating a successful scalable 3D ion trapping device is based on maintaining two qualities – the ability to scale the device to accommodate increasing numbers of atomic particles, whilst preserving the trapping potential which enables precise control of ions at the atomic level. Previous research resulted in compromising at least one of these factors, largely due to limitations in the manufacturing processes.

The team at NPL has now produced the first monolithic ion microtrap array which uniquely combines a near ideal 3D geometry with a scalable fabrication process – a breakthrough in this field. In terms of elementary operating characteristics, the microtrap chip outperforms all other scalable devices for ions.

The coherent control of quantum-entangled states of trapped ions has led to significant advances in quantum information, quantum simulation, quantum metrology and laboratory tests of quantum mechanics and relativity. All of the basic requirements for processing quantum information with arrays of ion-based quantum bits (qubits) have been proven in principle. However, so far, no more than 14 ion-based qubits have been entangled with the ion-trap approach, so there is a clear need for arrays of ion traps that can handle a much larger number of qubits. Traps consisting of a two-dimensional electrode array11 have undergone significant development, but three-dimensional trap geometries can create a superior confining potential. However, existing three-dimensional approaches, as used in the most advanced experiments with trap arrays cannot be scaled up to handle greatly increased numbers of ions. Here, we report a monolithic three-dimensional ion microtrap array etched from a silica-on-silicon wafer using conventional semiconductor fabrication technology. We have confined individual 88Sr+ ions and strings of up to 14 ions in a single segment of the array. We have measured motional frequencies, ion heating rates and storage times. Our results demonstrate that it should be possible to handle several tens of ion-based qubits with this approach

Concept of the monolithic microtrap array. a, Schematic showing a silicon substrate supporting silica layers on the front and back sides of the trap chip. Both the silica and the silicon are etched to create a clear aperture and the three-dimensional linear trap structure.

Using a novel process based on conventional semiconductor fabrication technology, scientists developed the microtrap device from a silica-on-silicon wafer. The team were able to confine individual and strings of up to 14 ions in a single segment of the array. The fabrication process should enable device scaling to handle greatly increased numbers of ions, whilst retaining the ability to individually control each of them.

Due to the enormous progress in nanotechnology, the power of classical processor chips has been scaled up according to Moore’s Law. Quantum processors are in their infancy, and the NPL device is a promising approach for advancing the scale of such chips for ion-based qubits.

Alastair Sinclair, Principal Scientist, NPL said:

“We managed to produce an essential device or tool, which is critical for state-of-the-art research and development in quantum technologies. This could be the basis of a future atomic clock device, with relevance for location, timing, navigation services or even the basis of a future quantum processor chip based on trapped ions, leading to a quantum computer and a quantum information network.”

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