Why do we need to use Cryogenic Components in Quantum Computing?

Quantum computing is the next generation of computing that uses quantum mechanics to solve massive and complex operations quickly. Quantum computers can be used to perform tasks and analyze datasets that even the most powerful supercomputers can not handle.

Instead of using regular bits, quantum computers use quantum bits or “Qubits” which can only be detected at extremely low energy levels and at temperatures close to absolute zero. Qubits are extremely delicate, requiring cryogenic temperatures for stability. This requires cryogenic refrigeration systems with multiple stages of cooling and numerous RF cryogenic cables of significant length, all of which introduce thermal noise, harming the integrity of the qubit. 

To be ‘read', a qubit must be isolated from all possible interference. The cryogenic chambers needed for this function can reach temperatures down to 4mK (milli-Kelvin). This can require thousands of cryogenic components that can function in this environment.

Quantum computing uses quantum phenomena such as superposition and entanglement to compute data. Quantum computers utilize technology platforms such as super conducting circuits and trapped atomic ions.

Click here for details on Quantum entanglement.

In classical computing, the basic unit of information is simply called “bit” which can take up two values “0” or “1”. Like classical bits, Qubits can also take the value of 0 and 1 but what differentiates qubits from classical bits is that Qubits can take the value of 0 and 1 simultaneously. This occurs due to superposition and this property is elemental to quantum computing and quantum mechanics overall. Continuing with the correlation between classical bits and qubits, classical bits are excited and controlled using DC voltage while qubits can be excited using microwaves and magnetic fields. Each qubit requires an external RF circuitry to be controlled.

We know that quantum state is extremely fragile, and it requires cryogenic temperatures to reduce atomic movement and provide a vibration-free environment. Cryogenic conditions are required because thermal energy and subsequent vibrations can disturb quantum operations. Thermal energy can also introduce unwanted internal RF transitions. This is where the need for cryogenic RF components arises in quantum computing. Classical electronics and RF circuitry are usually designed to operate at temperatures ranging from -40°C to +80°C. This is a decent operating temperature for most commercial, military, and industrial applications; however, it is nowhere near the cryogenic temperature that is required to keep a quantum system stable. A cryogenic system can require temperatures as low as 4mK (-273 Degrees C).

Let us better visualize the current working of quantum computing. The quantum system is placed in a well isolated room where cryogenic environment is maintained, the RF circuitry is placed in another room where room temperature is maintained. These two are connected by RF Connectors and cables, which by nature, introduces losses and increases system complexity.

A real life quantum computer architecture with temperatures
 (Credits: Edoardo Charbon)

To overcome these challenges, there is a need for cryogenic RF components in quantum computing. An increase in availability and development of cryogenic RF components will enable the RF circuitry to be placed alongside the quantum system. A recent experiment needed 200 wideband coaxial cables, 45 microwave circulators, and numerous room-temperature electronics to control just 53 qubits.

Video on How to Make a Quantum Bit