<p>In this study, we investigate the emergence of the quantum boomerang effect in discrete-time quantum walks (DTQWs) subjected to random phase disorder. Our analysis shows that this effect can arise solely from the bias induced by the coin degree of freedom of the DTQW, without requiring external bias or asymmetry. We explore the evolution of the mean position of the quantum walker, denoted as <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(\overline{X}(t)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mover> <mi>X</mi> <mo>¯</mo> </mover> <mrow> <mo stretchy="false">(</mo> <mi>t</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>, under various initial conditions of the walker and quantum coin operators. The results indicate a significant dependence of the observed phenomena on the choice of initial state, enabling the selective induction of the quantum boomerang effect in both or only one portion of the wavepacket associated with specific internal states. By varying the quantum coin parameter <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(\theta \)</EquationSource> <EquationSource Format="MATHML"><math> <mi>θ</mi> </math></EquationSource> </InlineEquation>, we find that the maximum mean position follows a power-law decay near the Pauli-Z coin, characterized by <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(X_{\text {Max}} \sim \theta ^{-2}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>X</mi> <mtext>Max</mtext> </msub> <mo>∼</mo> <msup> <mi>θ</mi> <mrow> <mo>-</mo> <mn>2</mn> </mrow> </msup> </mrow> </math></EquationSource> </InlineEquation>. Additionally, we identify a scaling behavior <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(X_{\text {Max}} \sim W^{-2}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>X</mi> <mtext>Max</mtext> </msub> <mo>∼</mo> <msup> <mi>W</mi> <mrow> <mo>-</mo> <mn>2</mn> </mrow> </msup> </mrow> </math></EquationSource> </InlineEquation>, which is consistent with the localization length observed in disordered quantum systems.</p>

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Boomerang quantum walks

  • A. R. C. Buarque,
  • W. S. Dias,
  • Ernesto P. Raposo

摘要

In this study, we investigate the emergence of the quantum boomerang effect in discrete-time quantum walks (DTQWs) subjected to random phase disorder. Our analysis shows that this effect can arise solely from the bias induced by the coin degree of freedom of the DTQW, without requiring external bias or asymmetry. We explore the evolution of the mean position of the quantum walker, denoted as \(\overline{X}(t)\) X ¯ ( t ) , under various initial conditions of the walker and quantum coin operators. The results indicate a significant dependence of the observed phenomena on the choice of initial state, enabling the selective induction of the quantum boomerang effect in both or only one portion of the wavepacket associated with specific internal states. By varying the quantum coin parameter \(\theta \) θ , we find that the maximum mean position follows a power-law decay near the Pauli-Z coin, characterized by \(X_{\text {Max}} \sim \theta ^{-2}\) X Max θ - 2 . Additionally, we identify a scaling behavior \(X_{\text {Max}} \sim W^{-2}\) X Max W - 2 , which is consistent with the localization length observed in disordered quantum systems.