12 research outputs found
Information transfer by quantum matterwave modulation
Classical communication schemes that exploit wave modulation are the basis of
the information era. The transfer of information based on the quantum
properties of photons revolutionized these modern communication techniques.
Here we demonstrate that also matterwaves can be applied for information
transfer and that their quantum nature provides a high level of security. Our
technique allows transmitting a message by a non-trivial modulation of an
electron matterwave in a biprism interferometer. The data is encoded by a Wien
filter introducing a longitudinal shift between separated matterwave packets.
The transmission receiver is a delay line detector performing a dynamic
contrast analysis of the fringe pattern. Our method relies on the Aharonov-Bohm
effect and has no light optical analog since it does not shift the phase of the
electron interference. A passive eavesdropping attack will cause decoherence
and terminating the data transfer. This is demonstrated by introducing a
semiconducting surface that disturbs the quantum state by Coulomb interaction
and reduces the contrast. We also present a key distribution protocol based on
the quantum nature of the matterwaves that can reveal active eavesdropping
Quantenphysikalische Methoden zur Datenübertragung mit Elektronen-Materiewellen
Sichere Datenübertragung ist essentiell in unserer heutigen Zeit. Informationsaus-
tausch bestimmt unser wirtschaftliches und auch unser persönliches Leben. Noch
werden unsere Daten mit mathematischen Verschlüsselungsmethoden geschützt.
Mit der stetigen Weiterentwicklung der Quantencomputer ist es jedoch nur noch
eine Frage der Zeit bis jede Verschlüsselung dekodiert werden kann. Abhilfe schafft
die Quantenkryptografie, in der die Verschlüsselung nicht auf Algorithmen sondern
auf quantenmechanischen Grundgesetzen basiert. In den letzten Jahren hat sich
die Quanten-Kommunikation durch einzelne bzw. verschränkte Photonen, stetig
weiterentwickelt. In dieser Arbeit werden die Grundlagen geschaffen, dieses Gebiet
auf Elektronen zu erweitern. Ein Ziel dieser Arbeit ist, einen supraleitenden Felde-
mitter zu entwickeln. Dazu wurde in Tübingen die Technik etabliert, reproduzierbar
Spitzen aus dem Supraleiter Niob herstellen zu können. Die Emission solcher Spit-
zen wurde bei Raumtemperatur auf ihre Kohärenz untersucht und es wurde eine
Halterung gebaut, mit der die Spitzen unterhalb der Sprungtemperatur gekühlt
werden können. Im Rahmen eines Aufenthaltes am Lawrence Berkeley National Lab,
USA, wurde ein Setup realisiert, womit die Emission einer supraleitenden Spitze
untersucht werden kann. Dabei liegt das Augenmerk auf der Energiebreite und der
Teilchenstatistik der Emission. Durch Korrelationsmessungen soll festgestellt werden,
ob die supraleitende Spitze verschränkte Elektronenpaare emittiert. Das andere Ziel
der Arbeit ist, eine neuartige, sichere Quantenmethode zur Datenübertragung zu
entwickeln, durch Modulation einer Materiewelle in einem Biprisma-Interferometer.
Der Sender ist dabei ein Wienfilter, der den Kontrast des Interferograms moduliert.
Die Phasenlage oder die Position des Streifenmusters ändert sich dabei nicht. Der
Empfänger ist ein Delay-Line-Detektor, der dynamisch den Kontrast misst. Für
dieses Ziel wurde die Elektronik eines bestehenden Experiments erneuert und eine
computergesteuerte Sendeeinheit gebaut. Eine Nachricht wurde erfolgreich übertra-
gen und der Aufbau hinsichtlich Geschwindigkeit und Stabilität untersucht. Um die
Sicherheit des Übertragungsschemas zu erhöhen, wurde eine Methode entwickelt
mit Ähnlichkeiten zum BB84-Protokoll für Photonen. Der Sicherheitsaspekt beruht
hierbei auf dem Welle-Teilchen-Dualismus, der Symmetrie der Wienkurve und der
Dekohärenz. Abschließend wird die Sicherheit bei verschiedenen Abhörangriffen
diskutiert und auch experimentell gezeigt, wie ein Angriff mit einem klassischen
Instrument die Übertragung aufgrund von Dekohärenz verhindert.Secure data transmission is essential in the present time. The exchange of information
determines not only our economical but also our personal lives. The secure data
transfer is based on mathematical encryption but with the continuous development
in quantum computing it is a question of time until every encryption can be
decoded. Quantum cryptography can remedy this situation where security is based
on fundamental quantum principles. In the last few years, quantum communication
based on single and entangled photon transfer has improved significantly. The
present work establishes fundamental research to extend these methods to electron
matterwaves. One goal in this thesis was to develop a superconducting nanotip field
emitter. Thereby, a technique was established in Tübingen to reproducibly prepare
nanotips from the superconducting material niobium. The coherent emission of the
field emitter at room temperature was studied and a tip holder for cooling the tip
to the transition temperature was build. As part of a research trip to the Lawrence
Berkeley National Lab, USA, a setup to investigate the superconducting properties
of a niobium tip was established. The focus was set on the energy width and the
emission statistics. The idea is to determine with electron correlation measurements
if a superconducting tip emits entangled electrons, in the form of Cooper-Pairs.
The other goal in this thesis was to develop a new secure quantum method for data
transmission by modulating a matterwave in a biprism interferometer. Thereby,
the message was binary encoded and transmitted by a Wien filter. It represents
the sender and modulates the contrast of the interferogram without changing the
phase or position of the fringes. The receiver is a delay-line-detector for a dynamical
contrast analysis. To realize such an instrument, the electrical components of an
existing setup were modified and a computer controlled interface was created. It
includes the sending and receiving electronics and software. With the established
setup it was possible to successfully send a message and the method was examined
for transmission speed and stability. To improve the security of the technique, a
transmission protocol, similar to the BB84-method for photons was developed.
The security aspect is based on the wave-particle-duality, the symmetry of the
Wien-curve and decoherence. Furthermore, the security aspect connected to various
eavesdropper attacks is discussed in detail. It is also experimentally demonstrated
how a tapping approach with a classical instrument would ultimately lead to
decoherence and stop the communication
Near-monochromatic tuneable cryogenic niobium electron field emitter
Creating, manipulating, and detecting coherent electrons is at the heart of
future quantum microscopy and spectroscopy technologies. Leveraging and
specifically altering the quantum features of an electron beam source at low
temperatures can enhance its emission properties. Here, we describe electron
field emission from a monocrystalline, superconducting niobium nanotip at a
temperature of 5.9 K. The emitted electron energy spectrum reveals an
ultra-narrow distribution down to 16 meV due to tunable resonant tunneling
field emission via localized band states at a nano-protrusion's apex and a
cut-off at the sharp low-temperature Fermi-edge. This is an order of magnitude
lower than for conventional field emission electron sources. The self-focusing
geometry of the tip leads to emission in an angle of 3.7 deg, a reduced
brightness of 3.8 x 10exp8 A/(m2 sr V), and a stability of hours at 4.1 nA beam
current and 69 meV energy width. This source will decrease the impact of lens
aberration and enable new modes in low-energy electron microscopy, electron
energy loss spectroscopy, and high-resolution vibrational spectroscopy.Comment: to be published in Phys. Rev. Lett. (2022
Data transmission by quantum matter wave modulation
Classical communication schemes exploiting wave modulation are the basis of our information era. Quantum information techniques with photons enable future secure data transfer in the dawn of decoding quantum computers. Here we demonstrate that also matter waves can be applied for secure data transfer. Our technique allows the transmission of a message by a quantum modulation of coherent electrons in a biprism interferometer. The data is encoded in the superposition state by a Wien filter introducing a longitudinal shift between separated matter wave packets. The transmission receiver is a delay line detector performing a dynamic contrast analysis of the fringe pattern. Our method relies on the Aharonov-Bohm effect but does not shift the phase. It is demonstrated that an eavesdropping attack will terminate the data transfer by disturbing the quantum state and introducing decoherence. Furthermore, we discuss the security limitations of the scheme due to the multi-particle aspect and propose the implementation of a key distribution protocol that can prevent active eavesdropping