Quantum computing at room temperature – Chiportal

U.S. military researchers predict that quantum computing circuits that will no longer need extremely low temperatures to function will become a reality in about a decade.

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For years solid state quantum technology that functions well at room temperature has seemed like a distant achievement. Although the application of transparent crystals with a lack of optical linearity has emerged in the world of science as the most likely basis for this milestone, the likelihood of such a system has always remained low. Now, U.S. military scientists have officially verified the feasibility of this approach. Researcher Dr. Kurt Jacobs of the U.S. Army Research Laboratory, in collaboration with researchers Dr. Mikkel Heuck and Professor Dirk Englund of the Massachusetts Institute of Technology, became the first to demonstrate the feasibility of a quantum logic gate consisting of photonic circuits and optical crystals.
“If future devices using quantum technologies need to be cooled to extremely low temperatures, this need will make them expensive, bulky and energy-hungry,” the lead researcher said. “Our research focuses on the development of future photonic circuits that can utilize the mechanism of quantum entanglement to develop quantum devices that operate at room temperature.” Quantum technology offers a variety of future advances in the fields of computing, communication and remote sensing.

In order to perform any action, ordinary computers operate on the basis of completely defined information. The information itself is stored in many bits, each of which can be turned on (1) or turned off (0). An ordinary computer, which receives input defined by bits, can process this input to create an answer, which is also given as a number. A standard computer processes one input at a time. In contrast, quantum computers store information in the form of qubits (qubits, wikipedia) that can be in a special state where they are both turned on and off at the same time. This mode allows a quantum computer to test the answers to a large number of input types simultaneously. Although such a computer cannot display all the answers at once, it can display the interrelationships between the different answers, a situation that allows certain problems to be solved much faster than in a normal computer.

Unfortunately, one of the significant disadvantages of quantum systems is the fragility of the special states of the qubits. Most of the hardware used in quantum technology must be kept at extremely cold temperatures – close to absolute zero – in order to prevent the destruction of these special situations following a reaction with the environment in which the computer is located. “Any reaction of a qubit with anything else in its environment will cause the destruction of its quantum state,” the researcher explains. “For example, if the environment is a particle gas, then keeping the system at a particularly low temperature will cause the gas molecules to move slowly so that they do not collide very frequently in the quantum circuits.”

Researchers have put a lot of effort into solving this problem, but a complete solution has not yet been found. Currently, photonic circuits that include non-linear optical crystals have emerged as the only plausible solution for the development of quantum computing combined with solid-state systems at room temperature. “Photonic circuits are a bit like electrical circuits, except for the fact that they use light instead of electrical signals,” the researcher notes. “For example, we can produce channels within a transparent material, channels through which photons can move, similar to electrical signals moving along electrically conductive wires.” Unlike quantum systems that use ions or atoms to store information, quantum systems that use photons can bypass the low temperature limit. However, the photons must still react with other photons in order to perform logical operations. This is the stage where nonlinear optical crystals come into action.

Researchers can create spaces within the crystals and these spaces are able to temporarily capture photons within them. Using this method, the quantum system can achieve two possible qubit states: a space that stores a photon (on) and a space without a photon (off). These qubits in turn can create quantum logic gates that produce the infrastructure for special situations. In other words, researchers can take advantage of the temporary state of space in a crystal (filled with a photon or empty) to represent a qubit. The logical gates function on the basis of two qubits together, creating a quantum intertwining between them. This interweaving is automatically generated in a quantum computer, and is the mechanism required to develop quantum approaches that can be used in sensing applications. However, scientists who support the idea of ​​creating quantum logic gates using nonlinear optical crystals have relied solely on the hypothesis – until now. Although this idea presents a great promise for the future, doubts still remain as to the ability of this method to lead to the development of practical logical gates. The application of nonlinear optical crystals was in question until the researchers presented a way to apply a quantum logic gate using this approach based on existing components of quantum gates. “The problem was that if a single photon was moving inside a channel, that photon would carry behind it a ‘wave package’ of a defined shape,” explains the lead researcher. “For a quantum gate, it is necessary that the photonic wave packets remain the same even after the gate is activated. Since a lack of linearity destroys the wave packets, the question was whether we could fill the space in the wave packet, cause them to respond non-linearly and then cause the photons to be emitted again while preserving the original shape of the wave packet. Once they designed the appropriate quantum logic gate, the researchers performed a number of computer simulations of the gate operation to demonstrate that such a system could, in theory, function as required.

Practical construction of a quantum logic gate using this method will first of all require significant improvements in the quality of certain photonic components, the researchers explain. “Based on the progress made over the past decade, we anticipate that we will need another decade to achieve the required improvements,” the researcher said. “At the same time, the process of charging and emitting a wave package without distorting its shape is the process that will allow us to achieve this technology, which today is purely theoretical.”

The findings of the study have long been published in the scientific journal Physical Review Letters.

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