Avoiding leakage and errors caused by unwanted transitions in Lambda systems

Abstract

Three-level Lambda systems appear in various quantum information processing platforms. In several control schemes, the excited level serves as an auxiliary state for implementing gate operations between the lower qubit states. However, extra excited levels give rise to unwanted transitions that cause leakage and other errors, degrading the gate fidelity. We focus on a coherent-population-trapping scheme for gates and design protocols that reduce the effects of the unwanted off-resonant couplings and improve the gate performance up to several orders of magnitude. For a particular setup of unwanted couplings, we find an exact solution, which leads to error-free gate operations via only a static detuning modification. In the general case, we improve gate operations by adding corrective modulations to the pulses, thereby generalizing the DRAG protocol to Lambda systems. Our techniques enable fast and high-fidelity gates and apply to a wide range of optically driven platforms, such as quantum dots, color centers, and trapped ions.

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• Time-bin entanglement in the deterministic generation of linear photonic cluster states
• Suppressing spurious transitions using spectrally balanced pulse
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• Giant Rabi frequencies between qubit and excited hole states in silicon quantum dots
• Incorporation of random alloy GaBi${}_x$As${}_{1-x}$ barriers in InAs quantum dot molecules: alloy strain and orbital effects towards enhanced tunneling
• Incoherent Approximation of Leakage in Quantum Error Correction