progress report: tools for quantum information processing in microelectronics
DESCRIPTION
Progress Report: Tools for Quantum Information Processing in Microelectronics ARO MURI (Rochester-Stanford-Harvard-Rutgers) Third Year Review, Harvard University, February 25-26, 2001 C. M. Marcus, Harvard University http://marcuslab.harvard.edu - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Progress Report: Tools for Quantum Information Processing in Microelectronics](https://reader035.vdocuments.us/reader035/viewer/2022062518/56814400550346895db0960e/html5/thumbnails/1.jpg)
Progress Report:Tools for Quantum Information Processing in
Microelectronics
ARO MURI (Rochester-Stanford-Harvard-Rutgers)
Third Year Review, Harvard University, February 25-26, 2001C. M. Marcus, Harvard University
http://marcuslab.harvard.edu
1) Understanding (finally) how 0.7 structure in quantum point contacts can be used as a natural spin system.
2) First results on multiple point contact systems - toward spin entangled chains.
3) Using a quantum dot as a gate-tunable spin filter. First experiments.
4) The next steps.
![Page 2: Progress Report: Tools for Quantum Information Processing in Microelectronics](https://reader035.vdocuments.us/reader035/viewer/2022062518/56814400550346895db0960e/html5/thumbnails/2.jpg)
Quantized Conductance
(data from vanWees, 1988)
![Page 3: Progress Report: Tools for Quantum Information Processing in Microelectronics](https://reader035.vdocuments.us/reader035/viewer/2022062518/56814400550346895db0960e/html5/thumbnails/3.jpg)
![Page 4: Progress Report: Tools for Quantum Information Processing in Microelectronics](https://reader035.vdocuments.us/reader035/viewer/2022062518/56814400550346895db0960e/html5/thumbnails/4.jpg)
In-plane magnetic field dependence
![Page 5: Progress Report: Tools for Quantum Information Processing in Microelectronics](https://reader035.vdocuments.us/reader035/viewer/2022062518/56814400550346895db0960e/html5/thumbnails/5.jpg)
temperature dependence
0.7 feature gets stronger at higher temperatures!
![Page 6: Progress Report: Tools for Quantum Information Processing in Microelectronics](https://reader035.vdocuments.us/reader035/viewer/2022062518/56814400550346895db0960e/html5/thumbnails/6.jpg)
![Page 7: Progress Report: Tools for Quantum Information Processing in Microelectronics](https://reader035.vdocuments.us/reader035/viewer/2022062518/56814400550346895db0960e/html5/thumbnails/7.jpg)
3
2
1
0-1 0 1
Vsd (mV)
T = 75 mK, B|| = 8 T3
2
1
0-1 0 1
Vsd (mV)
T = 75 mK, B|| = 0 T
3
2
1
0-1 0 1
Vsd (mV)
T = 600 mK, B|| = 0 T T=80mK B=8TT = 0.6K B=0T = 80mK B=0
g g g
Vsd Vsd Vsd
Nonlinear Transport
![Page 8: Progress Report: Tools for Quantum Information Processing in Microelectronics](https://reader035.vdocuments.us/reader035/viewer/2022062518/56814400550346895db0960e/html5/thumbnails/8.jpg)
3
2
1
0-1 0 1
Vsd (mV)
T = 75 mK, B|| = 8 T3
2
1
0-1 0 1
Vsd (mV)
T = 75 mK, B|| = 0 T
3
2
1
0-1 0 1
Vsd (mV)
T = 600 mK, B|| = 0 T T=80mK B=8TT = 0.6K B=0T = 80mK B=0
g g g
Vsd Vsd Vsd
Nonlinear Transport
![Page 9: Progress Report: Tools for Quantum Information Processing in Microelectronics](https://reader035.vdocuments.us/reader035/viewer/2022062518/56814400550346895db0960e/html5/thumbnails/9.jpg)
3
2
1
0-1 0 1
Vsd (mV)
T = 75 mK, B|| = 8 T3
2
1
0-1 0 1
Vsd (mV)
T = 75 mK, B|| = 0 T
3
2
1
0-1 0 1
Vsd (mV)
T = 600 mK, B|| = 0 T T=80mK B=8TT = 0.6K B=0T = 80mK B=0
g g g
Vsd Vsd Vsd
Nonlinear Transport
![Page 10: Progress Report: Tools for Quantum Information Processing in Microelectronics](https://reader035.vdocuments.us/reader035/viewer/2022062518/56814400550346895db0960e/html5/thumbnails/10.jpg)
3
2
1
0-1 0 1
Vsd (mV)
T = 75 mK, B|| = 8 T3
2
1
0-1 0 1
Vsd (mV)
T = 75 mK, B|| = 0 T
3
2
1
0-1 0 1
Vsd (mV)
T = 600 mK, B|| = 0 T T=80mK B=8TT = 0.6K B=0T = 80mK B=0
g g g
Vsd Vsd Vsd
Nonlinear Transport
![Page 11: Progress Report: Tools for Quantum Information Processing in Microelectronics](https://reader035.vdocuments.us/reader035/viewer/2022062518/56814400550346895db0960e/html5/thumbnails/11.jpg)
quantum dot quantum point contact
gate
2DEG2DEG
gate
Lifting spin degeneracy due to interactions
![Page 12: Progress Report: Tools for Quantum Information Processing in Microelectronics](https://reader035.vdocuments.us/reader035/viewer/2022062518/56814400550346895db0960e/html5/thumbnails/12.jpg)
Kondo Effect in Metals
![Page 13: Progress Report: Tools for Quantum Information Processing in Microelectronics](https://reader035.vdocuments.us/reader035/viewer/2022062518/56814400550346895db0960e/html5/thumbnails/13.jpg)
Kondo Effect in Quantum Dots
![Page 14: Progress Report: Tools for Quantum Information Processing in Microelectronics](https://reader035.vdocuments.us/reader035/viewer/2022062518/56814400550346895db0960e/html5/thumbnails/14.jpg)
Kondo Effect in Quantum Dots
Cronenwett, et al (Delft)
![Page 15: Progress Report: Tools for Quantum Information Processing in Microelectronics](https://reader035.vdocuments.us/reader035/viewer/2022062518/56814400550346895db0960e/html5/thumbnails/15.jpg)
Now, back to our quantum point contact
![Page 16: Progress Report: Tools for Quantum Information Processing in Microelectronics](https://reader035.vdocuments.us/reader035/viewer/2022062518/56814400550346895db0960e/html5/thumbnails/16.jpg)
Kondo-like scaling in a quantum point contact
![Page 17: Progress Report: Tools for Quantum Information Processing in Microelectronics](https://reader035.vdocuments.us/reader035/viewer/2022062518/56814400550346895db0960e/html5/thumbnails/17.jpg)
Kondo Temperature and Transport Features
![Page 18: Progress Report: Tools for Quantum Information Processing in Microelectronics](https://reader035.vdocuments.us/reader035/viewer/2022062518/56814400550346895db0960e/html5/thumbnails/18.jpg)
In-Plane FieldDependence ofZero Bias Anomaly
![Page 19: Progress Report: Tools for Quantum Information Processing in Microelectronics](https://reader035.vdocuments.us/reader035/viewer/2022062518/56814400550346895db0960e/html5/thumbnails/19.jpg)
g
Vsd
B|| = 0
B|| = 3T
B|| = 8T
![Page 20: Progress Report: Tools for Quantum Information Processing in Microelectronics](https://reader035.vdocuments.us/reader035/viewer/2022062518/56814400550346895db0960e/html5/thumbnails/20.jpg)
quantum dot quantum point contact
Charging energy lifts spin degeneracy. Kondo effect results from interaction ofunpaired state with leads.
Interaction energy lifts spin degeneracy. Kondo effect results from interaction ofunpaired mode with bulk 2DEG.
gate
2DEG2DEG
gate
![Page 21: Progress Report: Tools for Quantum Information Processing in Microelectronics](https://reader035.vdocuments.us/reader035/viewer/2022062518/56814400550346895db0960e/html5/thumbnails/21.jpg)
entanglement of 1 and 2
propagation ofentanglement
exact numericalfor N=31
long-chain limit
![Page 22: Progress Report: Tools for Quantum Information Processing in Microelectronics](https://reader035.vdocuments.us/reader035/viewer/2022062518/56814400550346895db0960e/html5/thumbnails/22.jpg)
2 m
KONDO
A single quantum point contact acts as a free spin with a Kondo-like screening cloud at low temperature
what happens when more than one point contact are in proximity?
![Page 23: Progress Report: Tools for Quantum Information Processing in Microelectronics](https://reader035.vdocuments.us/reader035/viewer/2022062518/56814400550346895db0960e/html5/thumbnails/23.jpg)
2 m
RKKY
KONDO
KONDO
Depending on parameters, the quasibound spins should become entangled with each other, mediated by conduction electrons.
This is the famous RKKY interaction, the physical effectthat gives rise to spin glasses in 2D and 3D.
![Page 24: Progress Report: Tools for Quantum Information Processing in Microelectronics](https://reader035.vdocuments.us/reader035/viewer/2022062518/56814400550346895db0960e/html5/thumbnails/24.jpg)
2 m
RKKY
RKKY
RKKY
KONDO
KONDO
KONDO
KONDO
We can use this to construct spin chains with controllable local Kondo temperatures
![Page 25: Progress Report: Tools for Quantum Information Processing in Microelectronics](https://reader035.vdocuments.us/reader035/viewer/2022062518/56814400550346895db0960e/html5/thumbnails/25.jpg)
B||
first experimental results:two point contacts in series
striking dependence onin-plane magnetic fieldindicates spin-related effect,but they are not understood.
![Page 26: Progress Report: Tools for Quantum Information Processing in Microelectronics](https://reader035.vdocuments.us/reader035/viewer/2022062518/56814400550346895db0960e/html5/thumbnails/26.jpg)
Point contact at 1e2/h plateau as spin detector
B|| = 8T
N even to N oddS→ +1/2S
N odd to N evenS→ -1/2S
Aligned spins transmitted - Anti aligned spins transmitted
B||
A spin separatorand spin-bridge detector
2) quantum dot as gate-tunable spin filter
1 m
![Page 27: Progress Report: Tools for Quantum Information Processing in Microelectronics](https://reader035.vdocuments.us/reader035/viewer/2022062518/56814400550346895db0960e/html5/thumbnails/27.jpg)
2.5
2.0
1.5
1.0
0.5
-200 -100 0 100 200Gate Voltage (mV)
Vg(mV)
g (e
2 /h)
0.25
0.20
0.15
0.10
0.05
0.00403020100
Gate Voltage (mV)
g (e
2 /h)
Vg(mV)
First Data on Spin Injection and Detection from a QD
Telectron~150mKBparallel = 7T
![Page 28: Progress Report: Tools for Quantum Information Processing in Microelectronics](https://reader035.vdocuments.us/reader035/viewer/2022062518/56814400550346895db0960e/html5/thumbnails/28.jpg)
0.25
0.20
0.15
0.10
0.05
0.00403020100
Gate Voltage (mV)
200x10-9
150
100
50
0
403020100Gate Voltage (mV)
gQPC ~ 1e2/h
0.25
0.20
0.15
0.10
0.05
0.00403020100
Gate Voltage (mV)
200x10-9
150
100
50
0
403020100Gate Voltage (mV)
gQPC ~ 2e2/h
Vg(mV)
Vg(mV) Vg(mV)
Vg(mV)
conductance
conductance
focusing
focusing
g (e
2 /h)
g (e
2 /h)
![Page 29: Progress Report: Tools for Quantum Information Processing in Microelectronics](https://reader035.vdocuments.us/reader035/viewer/2022062518/56814400550346895db0960e/html5/thumbnails/29.jpg)
Significant Results in the last 12 months:
Breakthrough in understanding of 0.7 structure in a quantum point contact: Free spin, due to interactions, capable of undergoing Kondo screening. (Cronenwett, et al., PRL, in press.)
First results on arrays of quantum point contacts, clear evidence of spin physics, but still lacking a good physical picture. Arrays of point contacts can be used to realize propagation of spin entanglement.
Focusing from a quantum dot into a quantum point contact as a demonstration of gate-controlled spin filtering has first hurdle passed: strong focusing signal from a quantum dot. Experiments underway.
![Page 30: Progress Report: Tools for Quantum Information Processing in Microelectronics](https://reader035.vdocuments.us/reader035/viewer/2022062518/56814400550346895db0960e/html5/thumbnails/30.jpg)
The next year:
•Construct spin chains with gated regions between point contacts to change density and multiple ohmic contact points.
•Develop noise measurement technology in our lab. Measure noise cross-correlation to investigate correlations between quantum point contacts.
•Complete first dot-focusing experiments, investigate size and temperature dependence. Compare to direct ground state spin measurements to see if multi-electron dots can operate as spin filters and spin storage devices.
•Begin to investigate variable g-factor materials with simple point contacts and quantum dots.