Quantum pathology of static internal imperfections in flawed quantum computers

Abstract

Even in the absence of external influences the operability of a quantum computer (QC) is not guaranteed because of the effects of residual oneand two-body imperfections. Here we investigate how these internal flaws affect the performance of a quantum controlled-NOT (CNOT) gate in an isolated flawed QC. First we find that the performance of the CNOT gate is considerably better when the two-body imperfections are strong. Secondly, we find that the largest source of error is due to a coherent shift rather than decoherence or dissipation. Our results suggest that the problem of internal imperfections should be given much more attention in designing scalable QC architectures.

Kraus decomposition for chaotic environments

“…This prediction is in agreement with that of an approximate master equation [8,9,22,23,24] which has been shown to be quantitatively accurate for a number of systems [8,9].…”

“…In our recent investigation [8] we showed that internal decoherence, dissipation and coherent shifting, caused by static one and two-body internal imperfections, are potential error sources for flawed QCs [31]. We also showed that a single detector qubit can be configured to probe internal bath dynamics [9] and thus one can obtain valuable information about the bath self-interactions.…”

“…Solid and condensed phase environments bequeath a diversity of controllable interactions for scalable implementation of new quantum technologies, and thus understanding the open system dynamics induced by such complex environments is of particular interest. Recent studies have reported a number of interesting effects such as suppression of decoherence with increasing bath chaos [6,7,8,9] and large coherent shifting [8,9].…”

“…But at the very low temperatures relevant to quantum computing technologies the options are more limited. There is a recently developed approximate master equation [8,9,22,23,24] which appears to be accurate in this low temperature regime. However, as with any approximate theory its predictions need to be otherwise confirmed.…”

Kraus decomposition for chaotic environments including time-dependent subsystem Hamiltonians

“…In other configurations, part of a QC can be employed to measure the strength of residual two-body interactions [3], and this knowledge may prove useful for error correction. Idle qubits can also be manipulated to improve performance of the active qubits [4,5]. In fact such self-interacting quantum systems have an exceedingly complex dynamics we are only beginning to explore.…”