Quantum Information Processing

, Volume 15, Issue 11, pp 4501–4520 | Cite as

Multifractality in fidelity sequences of optimized Toffoli gates

  • Jalil Khatibi Moqadam
  • Guilherme S. Welter
  • Paulo A. A. Esquef


We analyze the multifractality in the fidelity sequences of several engineered Toffoli gates. Using quantum control methods, we consider several optimization problems whose global solutions realize the gate in a chain of three qubits with XY Heisenberg interaction. Applying a minimum number of control pulses assuring a fidelity above 99 % in the ideal case, we design stable gates that are less sensitive to variations in the interqubits couplings. The most stable gate has the fidelity above 91 % with variations about 0.1 %, for up to 10 % variation in the nominal couplings. We perturb the system by introducing a single source of 1 / f noise that affects all the couplings. In order to quantify the performance of the proposed optimized gates, we calculate the fidelity of a large set of optimized gates under prescribed levels of coupling perturbation. Then, we run multifractal analysis on the sequence of attained fidelities. This way, gate performance can be assessed beyond mere average results, since the chosen multifractality measure (the width of the multifractal spectrum) encapsulates into a single performance indicator the spread of fidelity values around the mean and the presence of outliers. The higher the value of the performance indicator the more concentrated around the mean the fidelity values are and rarer is the occurrence of outliers. The results of the multifractal analysis on the fidelity sequences demonstrate the effectiveness of the proposed optimized gate implementations, in the sense they are rendered less sensitive to variations in the interqubits coupling strengths.


Quantum computation Quantum control Time series analysis 



JKM acknowledges Grants PCI-DB 302866/2014-0 and PDJ 165941/2014-6, and GSW and PAAE acknowledge Grant 475566/2012-2, from Brazilian National Council for Scientific and Technological Development (CNPq).


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Copyright information

© Springer Science+Business Media New York 2016

Authors and Affiliations

  • Jalil Khatibi Moqadam
    • 1
  • Guilherme S. Welter
    • 2
  • Paulo A. A. Esquef
    • 2
  1. 1.Instituto de Física “Gleb Wataghin”Universidade Estadual de CampinasCampinasBrazil
  2. 2.Laboratório Nacional de Computação Científica (LNCC)PetrópolisBrazil

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