Even minor but repeated disruptions can be enough to make quantum computers malfunction. Quantum computers could eventually solve challenging problems faster and more efficiently than today’s supercomputers, from simulating molecules to optimizing complex logistics.
Achieving this potential will require increasing the number of qubits, the fundamental units used to store and process quantum information. However, expanding quantum systems could create a significant challenge that researchers have largely overlooked.
Researchers at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) write in the New Journal of Physics that the quantum Zeno effect could, under extreme conditions, nearly halt quantum calculations as the number of qubits increases—similar to how a traditional computer can freeze or become unresponsive.
Adiabatic Quantum Designs Have a Hidden Limitation
Dr. Gernot Schaller, head of Quantum Technologies at HZDR’s Institute of Theoretical Physics, says the quantum Zeno effect represents a previously unrecognized challenge for certain types of quantum computers. The issue affects adiabatic quantum computers, which keep their qubits in the ground state—the lowest energy state available.
An adiabatic quantum computer performs calculations by gradually changing the energy landscape of its qubits. The system must evolve slowly enough to keep the qubits in the ground state throughout the process. Once the calculation finishes, this final ground state encodes the solution to the original problem.
According to Institute Director Prof. Ralf Schützhold, researchers consider adiabatic algorithms particularly robust because quantum computers can run them largely regardless of the underlying hardware. The same method can work with superconducting solid-state qubits or individual ions confined in electromagnetic traps. Researchers are already testing adiabatic algorithms on both platforms, and their relatively simple programming makes them an attractive approach.
Adding More Qubits can Intensify the Effects of Environmental Disturbances
“Still, quantum computers can operate reliably only when their qubits remain largely undisturbed,” Schützhold explains. To reduce interference, engineers shield qubits from electromagnetic radiation and cool them to temperatures approaching absolute zero, or −273.15 °C.
These measures help maintain superposition, which allows a qubit to exist in a combination of states between 0 and 1. They also preserve entanglement, the extremely delicate quantum link between qubits. Together, these properties enable quantum computers to tackle certain complex problems at remarkable speeds.
“Despite these protective measures, it is impossible to completely shield qubits from environmental influences,” Schützhold says. His team’s theoretical model suggests that adiabatic quantum systems become increasingly sensitive to such disturbances as more qubits are linked together.
As the number of connected qubits grows, the system must respond to progressively smaller changes in its energy landscape. “This is where the quantum Zeno effect comes into play,” Schaller explains. Even minor environmental disturbances can then affect the qubits’ quantum states. Each disruption effectively acts as an unintended measurement, slowing the system’s evolution. Under extreme conditions, the calculation could come to a complete halt.
The researchers compare the phenomenon to baking a cake. A cake needs to remain undisturbed in the oven for enough time to rise properly. Opening the oven repeatedly to check on it interrupts the baking process and can leave the cake flat or cause it to collapse. Similarly, repeated disturbances can interfere with the natural evolution of a quantum state. If these interruptions occur frequently enough, the system may fail to reach its intended final state, causing the calculation to slow dramatically or nearly freeze.
Active Protection May Help Keep Quantum Computers From Freezing
Quantum computer developers could reduce this risk by strengthening protection against heat and electromagnetic radiation. Using the baking analogy, better shielding would be like securing the oven door so it cannot be opened over and over.
Schützhold also highlights active techniques that could help maintain the calculation. With the spin-echo method, researchers can apply carefully controlled pulses to weaken the interaction between qubits and their surrounding environment. In the oven comparison, this is similar to briefly raising the temperature whenever the door opens to compensate for the heat that escapes.
“Our findings show that building powerful quantum computers requires us to account for environmental effects from the outset,” Schützhold concludes.
Read the original article on: SciTechDaily
Read more: Cybernetic Resilience and Organizational Survival
