Page 166 - Principles and Applications of NanoMEMS Physics

154 Chapter 4

detection resolution of about 70 q / Hz . This device has the potential to
exploit charge discreteness effect.

4.2.2.2.2 Which-Path Electron Interferometer

Armour and Blencowe [177], [178] presented a theoretical analysis for
this concept. A cantilever resonator operating at radio frequencies is
disposed over one of the arms of an Aharonov-Bohm (AB) [125] ring
containing a quantum dot (QD), Figure 3-4. Electrostatic coupling of the
vibrating beam with

B otto
B ottom m
A haronov-B oh m R in
Electrode e A haronov-B oh m R ing g
Electrod
V DC + V AC
V DC + V AC
+ +
- -
Φ Φ
Beam
Beam
Resonator r
Resonato
Quantum m
Quantu
Do
Dot t
SID E VIE W
SID E VIE W
G G Φ Φ
E E
Quantu
Quantum m Substrate
Substrate
Dot t
Do
Figure 4-4. Schematic of mechanical which-path electron interferometer [22].
electrons hopping in/out of the QD modulates the interference fringes,
according to vibration frequency( )-electron dwell time,τ = = ∆ E ,
ω
0 d inc
product, where E∆ is the electron energy spread. For ω τ << 1, short
inc 0 d
dwell time, interference fringes are destroyed if qE∆ x > ∆ E ., where x
th inc th
is the thermal position uncertainty of the cantilever and E the electric field.
This signals electron dephasing and detection in QD arm. For ω τ ~ 1, the
0 d
beam-QD behaves as a coherent quantum system, beam vibration and QD
exchange virtual energy quanta in resonance, and interference fringes are
modulated at beam vibrating frequency. For the largest dwell times, the
environment induces lost of coherence. This device has the potential to
exploit charge discreteness effect.