حل تشریحی سوال شماره 22 زبان تخصصی (انگلیسی)

PASSAGE 3: Quantum computation is a field of much interest and activity. Much of the interest was stimulated by Shor's discovery that there is a quantum computation algorithm for the integer factoring problem that is more efficient than any known classical algorithm. [l] This result has stimulated much work that represents steps in the long-term goal of physical construction of quantum computers. This includes work on quantum error­ correction codes and physical models of quantum gates, quantum Hall systems, and nuclear magnetic resonance to carry out parallel quantum computation. The optimism about reaching the long-term goal that is implicit in this work is tempered by the work of Landauer. [2] As a critic, Landauer correctly points out the enormous obstacles in the path of construction of efficient quantum computers. These include effects of environmental noise with respect to which quantum computers are exquisitely sensitive, errors in constructing the Hamiltonian, and errors in constructing the initial state. As Landauer notes, these errors can cause unwanted reflections of the computational process that reduce the amplitude of the transmitted component that represents the completed computation. Work in which potential barriers causing reflection are introduced intentionally where the potential distribution is 'deterministically disordered', suggests that in some cases, these problems may be less severe than otherwise thought. Building quantum computers is incredibly difficult. Many candidate qubit systems exist on the scale of single atoms, and the physicists, engineers, and materials scientists who are trying to execute quantum operations on these systems constantly deal with two competing requirements. [3] First, qubits need to be protected from the environment because it can destroy the delicate quantum states needed for computation. The longer a qubit survives in its desired state the longer its "coherence time." From this perspective, isolation is prized. Second, however, for algorithm execution qubits need to be entangled, shuffled around physical architectures, and controllable on demand. The better these operations can be carried out the higher their "fidelity." [4]