By exact numerical and master equation approaches, we show that a central spin-1/2 can be configured to probe internal bath dynamics. System-bath interactions cause Rabi oscillations in the detector and periodic behavior of fidelity. This period is highly sensitive to the strength of the bath self-interactions, and can be used to calculate the intra-bath coupling

We consider a system interacting with a chaotic thermodynamic bath. We derive an explicit and exact Kraus operator sum representation (OSR) for the open system reduced density. The OSR preserves the Hermiticity, complete positivity and norm. We show that it is useful as a numerical tool by testing it against exact results for a qubit interacting with an isolated flawed quantum computer. We also discuss some interesting qualitative aspects of the OSR.

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.

The inevitable existence of static internal imperfections and residual interactions in some quantum computer architectures results in internal decoherence, dissipation and destructive unitary shifts of active algorithms. By exact numerical simulations, we determine the relative importance and origin of these errors for a Josephson charge-qubit quantum computer. In particular we determine that the dynamics of a CNOT gate interacting with its idle neighboring qubits via native residual coupling behaves much like a perturbed kicked top in the exponential decay regime, where fidelity decay is only weakly dependent on perturbation strength. This means that retroactive removal of gate errors (whether unitary or non-unitary) may not be possible, and that effective error correction schemes must operate concurrently with the implementation of subcomponents of the gate.

The interaction of a quantum system with its surrounding environment results in losses of quantum correlations in the state of the system due to a decoherence process. The origin of decoherence is often attributed to the system–environment entanglement, which is not the only source of decoherence, however. Here we show that environment-induced coherent quantum fluctuations, i.e. Lamb or Stark shift-like effects, can also lead to the emergence of decoherence, which we call an incoherence process, even in the absence of the system–environment entanglement. We isolate the incoherence process from a general decoherence dynamics and formulate the exact equation of motion governing the incoherence dynamics in the absence of entanglement-induced decoherence. We exemplify the incoherence dynamics for a number of different situations including chaotic, regular and decoherence-free environments.