Researchers report the fabrication and operation of a qubit in a double-quantum dot in a silicon/silicon–germanium (Si/SiGe) heterostructure in which the qubit states are singlet and triplet states of two electrons. The significant advance over previous work is that a proximal micromagnet is used to create a large local magnetic field difference between the two sides of the quantum dot, which increases the manipulability significantly without introducing measurable noise.
The integrated micromagnet provides a promising path toward fast manipulation in materials with small concentrations of nuclear spins, including both natural silicon (Si) and isotopically enriched 28S.
"The next steps in our research are to increase both the magnitude of the field difference between the quantum dots, and the number of qubits by increasing the number of quantum dots," Coppersmith tells Phys.org. "Both steps are being implemented in new devices that have been designed and are currently being fabricated. We're also working on other qubit implementations in silicon quantum dots all of which use electrical initialization, manipulation and readout, and therefore have the potential advantages of integrability and scalability." Moreover, Eriksson points out that being able to control local magnetic fields in a nanoelectronic device could be very useful for spintronics.
Arxiv - Two-axis control of a singlet-triplet qubit with an integrated micromagnet
Researchers demonstrate coherent quantum control around two axes of the Bloch sphere of a singlet-triplet qubit in a silicon quantum dot. The relatively large magnetic field difference between the dots required to achieve two-axis control is implemented using a proximal micromagnet. By measuring the inhomogeneous spin coherence time T∗2 at many different values of the exchange coupling J and two different ∆B fields, we provide evidence that the dominant limits on T∗2 arise from charge noise and from coupling to nuclear spins.
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The integrated micromagnet provides a promising path toward fast manipulation in materials with small concentrations of nuclear spins, including both natural silicon (Si) and isotopically enriched 28S.
"The next steps in our research are to increase both the magnitude of the field difference between the quantum dots, and the number of qubits by increasing the number of quantum dots," Coppersmith tells Phys.org. "Both steps are being implemented in new devices that have been designed and are currently being fabricated. We're also working on other qubit implementations in silicon quantum dots all of which use electrical initialization, manipulation and readout, and therefore have the potential advantages of integrability and scalability." Moreover, Eriksson points out that being able to control local magnetic fields in a nanoelectronic device could be very useful for spintronics.
Arxiv - Two-axis control of a singlet-triplet qubit with an integrated micromagnet
Researchers demonstrate coherent quantum control around two axes of the Bloch sphere of a singlet-triplet qubit in a silicon quantum dot. The relatively large magnetic field difference between the dots required to achieve two-axis control is implemented using a proximal micromagnet. By measuring the inhomogeneous spin coherence time T∗2 at many different values of the exchange coupling J and two different ∆B fields, we provide evidence that the dominant limits on T∗2 arise from charge noise and from coupling to nuclear spins.
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