Quantum communication Archives

Comparison, specifications, and a comparison of the quantum field effect transistor (QFET) to the quantum coupled transistor (QCT)

Early design study, the novel Quantum Coupled Transistor, resembling a mirrored point contact transistor from 1947

Part I. Comparative Framework: QCT vs. QFET

Conduction Mechanisms
Coupling Types
Material Stacks
Operating Regimes
Functional Behavior
Conceptual Shift
→ Amplifying Evanescent Fields
(a) Recovering Lost Information
(b) Enabling Phase-Coupled Communication
(c) Accessing Hidden Quantum Channels

1. Conduction Mechanism

A Quantum Field-Effect Transistor (QFET) modulates the potential in a quantum well or two-dimensional electron gas (2DEG) channel through an electric field. Conduction still occurs through a continuous semiconductor layer such as GaAs, InP, or MoS₂.

In contrast, the Quantum-Coupled Transistor (QCT) contains no continuous conductive channel. Two graphene layers are separated by an insulating h-BN barrier, and current flows only through quantum tunneling, not drift or diffusion.

In simple terms:

QFET: electrons move through a channel.
QCT: electrons appear through a barrier.

Each graphene sheet can be independently biased, effectively functioning as both electrode and gate analogue. Unlike conventional transistors, the QCT requires no additional control gate – its modulation arises directly from interlayer biasing and phase-coupled tunneling across the h-BN medium.

2. Coupling Type

In a QFET, coupling is electrostatic. The gate field modifies the carrier concentration in the channel, altering current flow.
In a QCT, coupling is quantum-mechanical, relying on wavefunction overlap across the barrier. The signal path is therefore:

QFET: electric field → charge density → current
QCT: field phase → tunneling resonance → tunneling probability

The QCT does not merely modulate how much current flows; it determines whether two quantum states can interact at all.

3. Material Stack

Layer	QFET	QCT
Channel	GaAs, InP, Si, MoS₂	Graphene (G₁/G₂)
Barrier	Oxide (Al₂O₃, HfO₂)	h-BN (1–5 nm), atomically flat and lattice-matched to graphene
Operating Field	Gate-induced electric field	Interlayer bias plus plasmonic field modes

While a QFET uses a gate dielectric to control the flow of carriers, the QCT uses the barrier itself as an active quantum medium.

4. Operating Regime

Property	QFET	QCT
Frequency	Tens to hundreds of GHz	10–50 THz (practical), up to 150 THz (intrinsic)
Coherence	None (classical drift)	Coherent tunneling resonance, phase-sensitive transport
Energy Scale	meV range	Tens to hundreds of meV (bias-tunable)
Signal Type	Charge current	Phase-coupled field (plasmon–phonon mode)

The QCT operates in a high-frequency, coherent regime where quantum phase relationships become the dominant control parameter.

5. Functional Behavior

Functionally, the QCT behaves less like an on-off switch and more like a resonant coupler or quantum mixer. By tuning the interlayer bias and the relative twist angle of the graphene sheets, the device can:

Selectively couple specific frequency bands (as in a terahertz heterodyne mixer)
Amplify coherence across the tunneling barrier
Serve as an ultrafast, low-noise quantum tunneling modulator

6. Conceptual Shift

The Quantum-Coupled Transistor represents a fundamental change in device philosophy:
from controlling charge within matter →
to controlling coherence between quantum states.

It is, in essence, a transistor reimagined as a quantum bridge – not a valve for electrons, but a tunable conduit for quantum phase.

Amplifying Evanescent Fields

Evanescent modes decay exponentially with distance, yet they carry critical phase information. In the QCT, amplifying these modes can extend coherence and reveal otherwise hidden channels of information transfer.

(a) Recovering Lost Information

Evanescent components encode high-spatial-frequency (fine-detail) information – Fourier components that fade rapidly. Amplifying them restores detail that would otherwise blur beyond the barrier.

(b) Enabling Phase-Coupled Communication

Across the h-BN barrier, the QCT signal is not a propagating current but a phase-locked near-field coupling. Amplifying this mode:

Strengthens modulation of tunneling probability
Increases signal-to-noise ratio for coherent effects
Potentially enables information transfer via phase coherence rather than direct current flow

(c) Accessing “Hidden” Quantum Channels

Evanescent fields represent the overlap between classical and quantum domains – traces of virtual photons, plasmonic tunneling, and nonlocal correlations. Amplifying them accesses these “hidden” channels, enabling interaction through non-radiative fields.

Mechanism: In the QCT, Negative Differential Resistance (NDR) or quantum feedback re-injects energy into the tunneling modes, sustaining evanescent coupling instead of allowing decay.

Essentially, amplifying the evanescent field means amplifying the void itself – reinforcing the invisible bridge where information resides but energy does not flow.

These properties suggest that the QCT is not merely a device but a testbed for deeper questions about quantum coherence and information flow – leading directly to the framework of Causal-Foliated Signaling.

Part II. Causal-Foliated Signaling (CFS)

Core Axioms
Kinematics and Dynamics
Quantum Rules and Conservation
Experimental Predictions
Test Protocols
Role of the QCT

This article is part of a series, all related to an unexplained sighting I had in 1986 in Ireland:

Tag: Quantum communication

The Quantum-Coupled Transistor (QCT): Amplifying the Void