Studies of Electron Spin in Gallium Arsenide Quantum

DotsDaniel Craft, Dr. John Colton,

Tyler Park, Phil White, Brigham Young University

Quantum Computing Quantum states are

the “1”s and “0”s of a classical computer

Certain tasks—like factoring large numbers—are exponentially faster

Must understand quantum states

Jun Li et al, Sci. Rep. 2012/02/10 online

Quantum Dots Tiny, energetically and spatially

constrained structures: 2-10 nm

Quantum computers with interacting quantum dots that have an extra electron

Fast, optical control

Evidence of long lifetimes relative to control

Zeeman Splitting and Electron Spin 

 % Pol=%Low-% High

Faraday Effect Linearly polarized

light rotates Must be parallel

with magnetic polarization of sample

More magnetic polarization means more rotation

Wikipedia: Faraday Effect

Power Stabilizer

B

Probe-942nm

AOM

Linear Polarizer

Photoelastic Modulator

Signal to Lockin amplifier

Chopper

SuperconductingMagnet Set-up

PolarizingBeam Splitter

BalancedDetector

Timing Sequence

Beginning of Period End of Period

Time

Pump Pulse

Probe Probe Probe Probe Probe Probe Probe Probe Probe Probe Probe

Expected Scan Results

T1=359 ns

0 500 1000 1500 2000 2500

-0.040-0.035-0.030-0.025-0.020-0.015-0.010-0.0050.0000.0050.0100.0150.0200.0250.0300.0350.0400.045

Lock

in S

igna

l

Time (ns)

T1 Decay Scan?

Probe out of pump

0 500 1000 1500 2000 2500-0.014

-0.012

-0.010

-0.008

-0.006

-0.004

-0.002

0.000

0.002

0.004

0.006

0.008

0.010

0.012

0.014

0.016

-0.04

-0.03

-0.02

-0.01

0.00

0.01

0.02

0.03

0.04

Blu

e

Bla

ck

Time (ns)

Magnetic Field Comparison

bk: 0 Tbl: 1 T

0 500 1000 1500 2000 2500-0.006

-0.004

-0.002

0.000

0.002

0.004

0.006

0.008

0.010

-0.04

-0.03

-0.02

-0.01

0.00

0.01

0.02

0.03

0.04

Blu

e

Bla

ck

Time (ns)

Temperature Comparison

bk: 10 Kbl: 5 K

Power Stabilizer

B

942 nm

AOM

Linear Polarizer

PEM

Signal to Lock-in Amplifier

Chopper

Sample

Electromagnet Set-up

BalancedDetectorPolarizing

Beam Splitter

Electromagnet Scan Goals Same oscillations?

Does frequency change with laser power?

Does it change with pump pulse width?

Conclusions Quantum computing potential

depends on understanding quantum dots

We measure spin lifetimes using the Faraday effect

We saw oscillating spin polarization instead of decay

We need to do further tests