Modeling Read-Out for Solid-State Quantum Computers in Silicon

Modeling Read-Out for Solid-State Quantum Computers in Silicon Vincent Conrad Supervisors: C. Pakes & L. Hollenberg

Introduction Solid-State Quantum Computers in Silicon Single Electron Transistors Modeling Read-Out Results & Conclusion Further Work

Solid-State Quantum Computers in Silicon Scalable Hard Qubits Kane Quantum Computer Spin-Qubit Buried Donor Charge Qubit Quantum Computer Charge-Qubit

Kane Quantum Computer

Kane Quantum Computer spin-qubit

Buried Donor Charge-Qubit Quantum Computer Charge-qubit

Single Electron Tunneling Potential Barriers Quantised energy levels Fermi Level of Source is lower then first unoccupied level of dot { Energy spacing must be greater then thermal smearing

Single Electron Tunneling Applying a potential shifts Fermi energy of source the dot’s energy levels. now higher then dot’s 1 st unoccupied energy level. An electron can now occupy the dot. Coulomb blockade prevents others.

SET Single-Electron Transistor control Including a control gate allows us to manipulate the island’s energy levels. source dot (island) drain controlled single electron tunneling

Orthodox SET theory The only quantized energy levels occur in the island. The time of electron tunneling through the barrier is assumed to be negligibly small. Coherent quantum processes consisting of several simultaneous tunneling events ("co-tunneling") are ignored. Energy stored in a capacitor Work done by tunneling events

SET Sensitivity conductance control gate voltage electron motion extremely sensitive to voltage variations on the island

Read-Out drain Single electron’s motion between dopants. Vary potential on the source island (control gate). Induced island charge. Require induced charge > SET sensitivity. electron hole

Q = CV Spin-Qubit Read-Out

Q = CV Charge Qubit Read-Out

Results N. B. For charge qubit Dq is difference between two points. = 2. 49 x 10 -2 e = 2. 14 x 10 -2 e

Conclusions Induced island charge >> SET Sensitivity 2 x 10 -2 e >> 3. 2 x 10 -6 e Need an answer before information loss Electron-spin relaxation time (spin-qubit) Charge dissipation time (charge-qubit) Time given by shot-noise limit Well inside estimated times for both information loss mechanisms Both qubit types should produce measurable results using current technology made by the SRCQCT

Further Work More complete architecture simulations. Full type 3 simulation ISE-TCAD input files prepared. Estimate 100 000 node points required. Accounts and ISE-TCAD setup at HPC. Beowulf in-house cluster under construction. Matching simulations to experiment. Convert type 3 simulation to replicate macroscopic charge-qubit experiment.

A circuitry interlude: Nano-circuits are pretty darn small. Type 3 Device hole electron and hole (spin-qubit)

Integrated Systems Engineering – I S E Computer Technology – T C A D Aided Design coarse Poisson’s Equation Software package designed for microchip industry. User specifies mesh spacing to vary over MESH DESSIS PICASSO regions of interest. Graphical user interface for visual AC simulations. analysis of analysis Orthodox approach to single-electron tunneling. fine Extend ISE-TCAD to nanotech/mesoscopic devices.