Quantum chips need to be cooled because maintaining extremely low temperatures is crucial for preserving and manipulating the delicate quantum states of the qubits—the basic units of quantum information—on the chip. Cooling is necessary to minimize the effects of external disturbances and to prevent thermal noise from disrupting the fragile quantum coherence.
There are a few key reasons why cooling is essential for quantum chips:
Minimizing thermal noise: At higher temperatures, particles and their surroundings exhibit greater thermal motion, which can introduce random fluctuations and cause errors in the quantum computations. Cooling the chip reduces thermal noise and helps maintain the stability of the qubits.
Preserving quantum coherence: Quantum coherence refers to the fragile superposition and entanglement states that are crucial for quantum computation. These states are highly sensitive to environmental interactions and can quickly decohere, losing their quantum properties, when exposed to thermal energy. Cooling the chip to ultra-low temperatures helps to slow down decoherence, allowing quantum computations to be performed more reliably and over longer time scales.
Suppressing quantum effects from the environment: Cooling the chip helps suppress the influence of external factors such as electromagnetic radiation or vibrations that could disrupt the quantum states. Lower temperatures reduce the thermal energy available for interactions and isolate the qubits from their environment, providing a more controlled and stable quantum computing environment.
To achieve the necessary low temperatures, various cooling techniques are employed, depending on the specific quantum computing platform:
Dilution refrigeration: Dilution refrigeration is a common cooling technique used for superconducting qubits. It involves a multi-stage cooling process that uses a mixture of isotopes, such as helium-3 and helium-4, to reach temperatures close to absolute zero (near -273 degrees Celsius or -459 degrees Fahrenheit).
Cryogenic cooling: Cryogenic cooling involves using cryocoolers or cryostats to cool the quantum chip. These systems employ refrigeration techniques to achieve temperatures in the millikelvin range (a few thousandths of a degree above absolute zero).
Laser cooling: For certain types of qubits, such as trapped ions or neutral atoms, laser cooling techniques are utilized. By using precisely tuned lasers, the kinetic energy of the qubits can be reduced, effectively cooling them.
It's worth noting that cooling quantum chips is an ongoing area of research and development. Improvements in cooling technologies and materials may allow for more efficient cooling and better preservation of quantum states, ultimately contributing to the scalability and stability of quantum computers in the future.