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Integrated Qubits Towards Future High-Temperature Silicon Quantum Computing Hardware Technologies

Periodic Reporting for period 2 - IQubits (Integrated Qubits Towards Future High-Temperature Silicon Quantum Computing Hardware Technologies)

Período documentado: 2020-05-01 hasta 2021-10-31

At atomic scale, the fundamental building blocks of matter appear as discrete quantities, or quanta, which are commonly called elementary particles, as we study at school. These particles behave according to specific laws of Physics, known as Quantum Physics, different from those we have direct evidence in our everyday life, and that could appear to us as quite bizarre. The particles at atomic scale, like electrons, exhibit the so-called quantum effects, which depend on their quantum states. Two quantum states are very specific and attractive for us: superposition and entanglement. In analogy with our everyday life, superposition could be considered as the result of tossing a coin and, while spinning in the air, it is head and tail at the same time. During the entanglement state, two or more particles have a strong relationship and behave like a single entity. If entangled, anything happening to one of the particles will manifest instantaneously (in zero time!) to the others, even if they are very far from each other.
These quantum states can be manipulated through electronics circuits to execute a huge number of operations in a unit of time and, therefore, exploited to build very powerful computers, called quantum computers, which operate with the so-called quantum bits, or simply qubits, in analogy with bits in classical computers.

Quantum computers have the potential to solve computational problems that are unsolvable with the classical computers (including supercomputers) of today, such as the synthesis of new drugs to treat incurable diseases, understanding the secrets of the human brain, and many other open complex challenges in all fields of Science and Technology.

The current qubits are primarily developed in research laboratories and operate at extreme cryogenic temperatures of tens or hundreds milli-Kelvin, with electronic circuits for manipulation and readout that are external to the chip with the qubits, called quantum chip.
Just to have an idea, we can consider that the minimum temperature we can experience in our Universe is about 3 Kelvin, which is about minus 270 °C. Thereby, the extreme temperatures of the current qubits are way down the coldest temperature of our known Universe. Moreover, these qubits require electronic circuits external to the quantum chip.

The extreme cryogenic temperatures and the inherent limitations to the integration due to external electronic circuits, introduce dramatic barriers to the possibility to build actual quantum computers, with thousands and even million integrated qubits and circuits.

The general objective of the project IQubits is to break through these major scientific and technological barriers by developing integrated qubits, control and readout circuits that can operate at higher cryogenic temperatures and can be integrated together into the same chip in commercial nanoscale silicon technologies, so paving the way for moving quantum technologies out from research laboratories to semiconductor industry for large-scale fabrication of quantum processors.
In the first year (12 months) of the project, we have designed the preliminary qubits, control and readout circuits in a commercial nanoscale Silicon technology. We have identified the methodology about how to design these integrated qubits and circuits, as well as how to design more advanced and smaller qubits with 10nm characteristic dimension than those that can be fabricated today (22 nm) with the most advanced industrial silicon technology process that we believe has the capability to be a most suitable technology process for the implementation of future integrated quantum processors. We have started the development of the nanofabrication technology processes necessary for the fabrication of the advanced qubits capable of operating at higher temperature. At the same time, we have started the implementation of advanced simulation software capable of accounting for quantum effects at atomic scale, which are not taken into account in the current device and circuit design simulators of today.
In the second period (18 months), we have simulated, designed, fabricated and tested experimentally the preliminary qubits and qubit circuits in commercial nanoscale Silicon technology. The experimental measurements have shown that the transistors of some of advanced nanoscale commercial technologies provide clear evidences of quantum effects at cryogenic temperature. Also, verified that the design methodology for qubit control and readout ICs provides an effective design strategy. A large set of innovative and crucial building blocks have been designed, fabricated and verified experimentally with success, and their designs validated for the implementation of the final versions. The development of nano-fabrication processes for ultra-scaled devices with 10nm characteristic dimension have continued, and despite they still require further works, the results are promising.
The results show, for the first time, that the qubits implemented in the commercial 22nm silicon technology process, show superior quantum effects at acceptable cryogenic temperatures of a few Kelvin. An effective design methodology for the integrated circuits has been developed and proven experimentally through preliminary designs.
The results have been published and presented in the most relevant scientific journals and conferences.
In the next years, we expect to develop the hardware and software solutions that will allow proving the feasibility of advanced qubits and circuits of future integrated quantum processors that can operate at higher temperature, and can be designed with advanced software tools and fabricated on industrial scale.
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