Page 172 - Principles and Applications of NanoMEMS Physics

160 Chapter 4

vibration of the nanomechanical beam causes superposition of the field
produced by its ferromagnetic tip with the external magnetic field.
This results in a modulation of the magnetic field perceived by the nuclear
spins and, as a consequence, can stimulate transitions in the Larmor
frequency of nuclear spins (Zeeman effect). In turn, a dipolar interaction
couples the rotating transverse component of the nuclear magnetization of
the nuclear spins with the ferromagnetic tip, resulting in a force that drives
the beam oscillations. This process, under resonance between Larmor
frequency and beam vibration, leads to self-sustained ocillations, i.e., to laser
behavior. The proposed device was called “cantilaser.” Typical parameters are
as follows: Fundamental frequency of beam, 20 MHz, effective spring constant, 0.1
5
N/m, quality factor, 10 , transverse magnetic field gradient due to ferromagnetic
s
tip, 10 6 T / m , transverse relaxation time of nuclear spins, 50µ , nuclear
gyromagnetic ratio, 2 ×π 10 MHz / T , external magnetic field, 2 Tesla.

4.2.2.2.9 Quantum Entanglement Generation

As discussed in Chapter 3, quantum entanglement is a fundamental
ingredient for effecting quantum information processing. Most schemes for
quantum entanglement, however, were demonstrated in the context of optical
experiments, where the object of entanglement was photon polarization.
While the realm of implementation of NanoMEMS SoCs includes variants
that exploit optical signal processing, i.e., the processing and manipulation
of photons, electrons and, thus, electronic signal processing in solid-state
systems remain an important paradigm. It is not surprising, therefore, that a
number of efforts have been aimed at finding ways to achieve the electron
pair entanglement and transport over long distances. The superconductor-
carbon nanotube junction, proposed by Bena, Vishveshwara, Balents, and
Fisher [189] is a clever idea along these lines, see Fig. 4-9.

I A δ δ V
V A A
I A
SC
SC
A A
SW N
SW N T T
B B
I B δ δ V
I B
V B B
Figure 4-9. Quantum entanglement junction. A setup of two nanotubes A and B contacting a
superconductor. Voltage drops V A and V B may be preferentially applied across tubes A and B
respectively, and currents through each of them may be measured. [189].