  The linear energy-momentum dispersion, coupled with pseudo-spinors, makes
graphene an ideal solid-state material platform to realize an electronic device
based on Dirac-Fermionic relativistic quantum mechanics. Employing local gate
control, several examples of electronic devices based on Dirac fermion dynamics
have been demonstrated, including Klein tunneling, negative refraction and
specular Andreev reflection. In this work, we present a quantum switch based on
analogous Dirac-fermion-optics (DFO), in which the angle dependence of Klein
tunneling is explicitly utilized to build tunable collimators and reflectors
for the quantum wave function of Dirac fermions. We employ a novel dual-source
design with a single flat reflector, which minimizes diffusive edge scattering
and suppresses the background incoherent transmission. Our gate-tunable
collimator-reflector device design enables measurement of the net DFO
contribution in the switching device operation. We measure a full set of
transmission coefficients of DFO wavefunction between multiple leads of the
device, separating the classical contribution from that of any disorder in the
channel. Since the DFO quantum switch demonstrated in this work requires no
explicit energy gap, the switching operation is expected to be robust against
thermal fluctuations and inhomogeneity length scales comparable to the Fermi
wavelength. We find our quantum switch works at an elevated temperature up to
230 K and large bias current density up to 102 A/m, over a wide range of
carrier densities. The tunable collimator-reflector coupled with the conjugated
source electrodes developed in this work provides an additional component to
build more efficient DFO electronic devices.
