Abstract: A method of reducing quantum leakage in a qubit device which includes receiving a set of energy level values for a multi-level system which includes first and second working levels |0>, |1> which provide a qubit, and at least one other level |2>, and performing an iteration of determining quantum leakage from at least one of the first and second working levels to the at least one other level for a quantum operation A for at least one pulse wherein each pulse has a respective pulse duration, determining whether the quantum leakage is greater than or equal to a threshold value; and, based on the quantum leakage being greater than or equal to the threshold value, changing the duration of at least one of the at least one pulse.

Abstract: A silicon-based quantum dot device (1) is disclosed. The device comprises a substrate (8) and a layer (7) of silicon or silicon-germanium supported on the substrate which is configured to provide at least one quantum dot (51, 52: FIG. 5). The layer of silicon or silicon-germanium has a thickness of no more than ten monolayers. The layer of silicon or silicon-germanium may have a thickness of no more than eight or five monolayers.

Abstract: A method of reducing quantum leakage in a qubit device is disclosed. The method comprises receiving a set of energy level values for a multi-level system which includes first and second working levels |0>, |1> which provide a qubit and at least one other level |2> and performing an iteration at least once. the iteration comprising determining quantum leakage from at least one of the first and second working levels to the at least one non-working level for a quantum operation A comprising at least one pulse wherein each pulse has a respective pulse duration, determining whether the quantum leakage is greater than or equal to a threshold value; and, in dependence on the quantum leakage being greater than or equal to the threshold value, changing the duration of at least one of the at least one pulse.

Abstract: A silicon-based quantum dot device (1) is disclosed. The device comprises a substrate (8) and a layer (7) of silicon or silicon-germanium supported on the substrate which is configured to provide at least one quantum dot (51, 52: FIG. 5). The layer of silicon or silicon-germanium has a thickness of no more than ten monolayers. The layer of silicon or silicon-germanium may have a thickness of no more than eight or five monolayers.

Abstract: A device for sensing a magnetic field is described. The device comprises first, second and third leads and a junction between the leads. The junction and leads are arranged in a plane and the junction is configured to exhibit quantum confinement in a direction perpendicular to the plane. The first lead is arranged on one side of the junction and the second and third leads are arranged on an opposite side of the junction. The first lead is configured to limit angle of spread of charge carriers entering the junction so that, when charge carriers flow into the junction from the first lead, the charge carriers form a substantially nondivergent beam.

Abstract: A device for sensing a magnetic field is described. The device comprises first, second and third leads and a junction between the leads. The junction and leads are arranged in a plane and the junction is configured to exhibit quantum confinement in a direction perpendicular to the plane. The first lead is arranged on one side of the junction and the second and third leads are arranged on an opposite side of the junction. The first lead is configured to limit angle of spread of charge carriers entering the junction so that, when charge carriers flow into the junction from the first lead, the charge carriers form a substantially nondivergent beam.