Silicon quantum dots for quantum information processing€¦ · Quantum dot presents if electrons...
1
Silicon quantum dots for quantum information processing Silicon quantum dots for quantum information processing Author: Ross Leon Supervisor: Prof. Andrew Dzurak, Dr. Alessandro Rossi Research Theme: The Digital Future dot1 dot2 Background and Motivation |0> |1> Aim Quantum dot presents if electrons are confined in a small region and energy is discrete. Electrons have a spin property. Two electrons can be coupled to form a Qubit, representing logic. Electrons occupy different quantum dots when representing different logics, hence one can measure electron charge instead of spin, this is called spin-charge conversion. Double Quantum Dot (DQD) double reservoir system allows us to measure current directly, current resonate when quantum dot energy changes and number of electrons changes. To isolated electron in DQD, Single reservoir system forbid direct current measurement. Dot 1 Dot 1 Dot 2 Dot 2 Remotely detect movement of electrons across regions in a double dot single reservoir system Distinguish electron movements within different parts of the system Optimise detection quality by changing detector position Method General methodology to simulate the result is shown as follows: reservoir Dot 1 Dot 2 SET Principle of Operation C1 C2 reservoir Dot 1 Dot 2 SET dot1 dot2 I reservoir Results Single Electron Transistor (SET) has its own reservoirs with continuous current flow. Imbalance capacitance between each dot and SET induce different effect in SET current Changing charge occupancy of each dot will affect SET current, either by: 1. Applying voltage to each quantum dot 2. Electrons tunnel from one region to another 3D Design Capacitance Calculation Physical dimension 3D Model Capacitance Matrix Simulator Schematic Design Review Result Dot 1 FastCap: calculate mutual capacitance between all metals Simon: simulate quantum effect. Note: an equivalent schematic circuit of the quantum device is built to perform simulations of the electrical characteristics FCGUI2008 (Matlab program): 3D drawing I SET α β Results 2. Electron tunnelling detection Green and red lines in charge stability plot separates into regions with different electron numbers (Dot 1, Dot2). Number of electrons in both quantum dot in each Z-shape region are definite. Number of electrons in rhombus region in between depends on previous electron activities: In practice charge stability plot cannot be obtained. Measurement from SET detector current results in a saw- tooth shape due to: The magnitude of the charge sensing signal depends on distance between SET and each dot whose occupancy changes. Detector position: a. Vertical displacement i. Distance (hence capacitance) between each dot and SET becomes comparable, 1. Effect of Location of SET detector a. Loading electrons (eg. sweeping left to a. Either of the quantum dot voltages increase, result in oblique SET current. b. Electron ‘jump’ into/out of either quantum dot, causes vertical jump in SET current a b β α β becomes comparable, hence unable to distinguish different type of electrons tunnelling behaviours. right along blue dash line): only green lines in effect, ie. (M,N) b. Unloading electrons (eg. sweeping right to left along blue dash line) only red lines in effect, ie. (M,N+1) b. Horizontal displacement: i. SET current fluctuation magnitude is overwhelmed by background noise. ii. Similar to a(i), tunnelling behaviours cannot be γ α β α β γ recognised. Voltage sweep across black dash line results in all 3 types of electron tunnelling events. Different electron tunnelling events induce different magnitude of SET current jump. Conclusion SET can be used to detect electron tunnelling in double dot single reservoir system. Different electron tunnelling events can be distinguished by configuring SET detector location. This work has a significant impact in readout information from a spin qubit. To investigate spin charge conversion and conduct experiments to detect and deduce spin state of a quantum dot To control spin state of current quantum dot system, and store information before readout. Future Work reservoir Dot 1 Dot 2
Transcript of Silicon quantum dots for quantum information processing€¦ · Quantum dot presents if electrons...
Silicon quantum dots for quantum information processingSilicon quantum dots for quantum information processingAuthor: Ross Leon
Supervisor: Prof. Andrew Dzurak, Dr. Alessandro RossiResearch Theme: The Digital Future
dot1 dot2
Background and Motivation |0> |1>
Aim
�Quantum dot presents if electrons are confined in a small region and energy is discrete.�Electrons have a spin property. Two electrons can be coupled to form a Qubit, representing logic.�Electrons occupy different quantum dots when representing different logics, hence one can measure electroncharge instead of spin, this is called spin-charge conversion.�Double Quantum Dot (DQD) double reservoir system allows us to measure current directly, currentresonate when quantum dot energy changes and number of electrons changes.�To isolated electron in DQD, Single reservoir system forbid direct current measurement.
Dot 1 Dot 1Dot 2 Dot 2
Aim�Remotely detect movement of electrons across regions in adouble dot single reservoir system�Distinguish electron movements within different parts of thesystem�Optimise detection quality by changing detector position
Method
General methodology to simulate the result is shown as follows:
reservoir
Dot 1 Dot 2
SET
Principle of OperationC1 C2
reservoir
Dot 1 Dot 2
SET
dot1 dot2
I
reservoir
Results
�Single Electron Transistor (SET) has its own reservoirs with continuous current flow.�Imbalance capacitance between each dot and SETinduce different effect in SET current�Changing charge occupancy of each dot will affect SET current, either by:
1. Applying voltage to each quantum dot2. Electrons tunnel from one region to another
3D Design
Capacitance Calculation
Physical dimension
3D Model
Capacitance Matrix
Simulator
Schematic
Design
Review
Result
Dot 1FastCap: calculate mutual capacitance between all metals
Simon: simulate quantum effect. Note: an equivalent schematic circuit of the quantum device is built to perform simulations of the electrical characteristics
FCGUI2008 (Matlab program): 3D drawing
ISET
αβ
Results
2. Electron tunnelling detection
�Green and red lines in charge stability plot separates into regions with different electron numbers (Dot 1, Dot2).�Number of electrons in both quantum dot in each Z-shape region are definite.�Number of electrons in rhombus region in between depends on previous electron activities:
�In practice charge stability plot cannot be obtained.�Measurement from SET detector current results in a saw-tooth shape due to:The magnitude of the charge sensing signal depends on
distance between SET and each dot whose occupancy changes. Detector position:
a. Vertical displacementi. Distance (hence
capacitance) between each dot and SET becomes comparable,
1. Effect of Location of SET detector
a. Loading electrons (eg. sweeping left to
a. Either of the quantum dot voltages increase, result in oblique SET current.
b. Electron ‘jump’ into/out of either quantum dot, causes vertical jump in SET current
a b
β
α
β
becomes comparable, hence unable to distinguish different type of electrons tunnelling behaviours.
right along blue dash line): only green lines in effect, ie. (M,N)
b. Unloading electrons (eg. sweeping right to left along blue dash line) only red lines in effect, ie. (M,N+1)
b. Horizontal displacement:i. SET current fluctuation
magnitude is overwhelmed by background noise.
ii. Similar to a(i), tunnelling behaviours cannot be
γ
α
β
α
β
γ
behaviours cannot be recognised.
�Voltage sweep across black dash line results in all 3 types of electron tunnelling events.�Different electron tunnelling events induce different magnitude of SET current jump.
Conclusion
�SET can be used to detect electron tunnelling in double dot single reservoir system.�Different electron tunnelling events can be distinguished by configuring SET detector location.�This work has a significant impact in readout information from a spin qubit.
�To investigate spin charge conversion and conduct experiments to detect and deduce spinstate of a quantum dot�To control spin state of current quantum dot system, and store information before readout.
Future Work
reservoir Dot 1 Dot 2jump.
