102 research outputs found
Direct microwave measurement of Andreev-bound-state dynamics in a proximitized semiconducting nanowire
The modern understanding of the Josephson effect in mesosopic devices derives
from the physics of Andreev bound states, fermionic modes that are localized in
a superconducting weak link. Recently, Josephson junctions constructed using
semiconducting nanowires have led to the realization of superconducting qubits
with gate-tunable Josephson energies. We have used a microwave circuit QED
architecture to detect Andreev bound states in such a gate-tunable junction
based on an aluminum-proximitized InAs nanowire. We demonstrate coherent
manipulation of these bound states, and track the bound-state fermion parity in
real time. Individual parity-switching events due to non-equilibrium
quasiparticles are observed with a characteristic timescale . The of a topological nanowire
junction sets a lower bound on the bandwidth required for control of Majorana
bound states
Nanovezetékeken alapuló áramkörök gyártása és kvantum effektusainak elektron transzport vizsgálata = Fabrication and Electron Transport Study of Nanowire based Quantum Devices
Az anyagtudomány fejlĹ‘dĂ©sĂ©nek köszönhetĹ‘en számos nanomĂ©retű objektum lĂ©trehozására nyĂlik mĂłd napjainkban, ilyenek pĂ©ldául a fĂ©lvezetĹ‘ nanopálcák (NW). Kis mĂ©retĂĽk miatt ezek a NW-k nagyon ĂgĂ©retesek kvantum elektronikai cĂ©lokra. Kvantum elektronika a modern szilárdtestfizika dinamikusan fejlĹ‘dĹ‘ terĂĽlete, melynek fĹ‘ cĂ©lja elektromos áramkörök kvantum mechanikai szabadsági fokainak kontrollálása Ă©s kiolvasása, mint amilyen egy mestersĂ©ges atomba (QD) zárt elektron spinje. Jelen projektben nanomĂ©retű áramkörök kĂ©szĂtĂ©sĂ©re Ă©s kvantum effektusainak alacsony hĹ‘mĂ©rsĂ©kleti vizsgálatára alkalmas infrastruktĂşrát Ă©pĂtettĂĽnk ki. Vizsgáltuk InAs NW-kbĂłl Ă©s szupravezetĹ‘ (S) ill. ferromágneses (F) elektrĂłdák kombináciĂłjábĂłl kĂ©szĂtett áramköröket. InAs NW-ban kialakĂtott dupla kvantum dotot szupravezetĹ‘höz csatolva megmutattuk, hogy Cooper- párokat lehet tĂ©rben szeparálni, ami megnyitja az utat mobil elektronokbĂłl állĂł Einstein Podolsky Rosen párok keltĂ©sĂ©re Ă©s összefonĂłdottságuk tanulmányozására. MásrĂ©szrĹ‘l, ha F vezetĂ©ket kapcsolunk InAs NW-ban kialakĂtott QD-hoz, akkor a ferromágnessĂ©g lokális kicserĂ©lĹ‘dĂ©si tĂ©ret kelt a mestersĂ©ges atomon. Megmutattuk, hogy ez a tĂ©r erĹ‘sen fĂĽgg a QD töltĂ©s állapotátĂłl. SĹ‘t a tĂ©r mĂ©g elĹ‘jelet is válthat ugyanazon töltĂ©s állapotban, lehetĹ‘vĂ© tĂ©ve az alap állapot spinjĂ©nek megfordĂtását kapu feszĂĽltsĂ©g segĂtsĂ©gĂ©vel. Megmutattuk, hogy egy ilyen F-QD rendszer hatĂ©kony spin áram erĹ‘sĂtĹ‘kĂ©nt tud funkcionálni. | Recent development in material science allowed the synthesis of various nanoscale objects, like semiconductor nanowires (NW). Due to their small size, these NWs are very attractive for quantum electronic purpose. Quantum electronics is a dynamically progressing field of modern solid state physics, where the central goal is to manipulate and read out quantum mechanical degrees of freedom of circuits, like the spin of an electron trapped into a quantum dot (QD). In the present project the fabrication and transport characterization infrastructure have been established, which allows the production of nanocircuits and exploring their quantum effects in cryogenic measurements. We have investigated various InAs NW based electric circuits, where superconducting (S) and ferromagnetic (F) leads were attached to the wire. Coupling S lead to NW based double QD system, we have demonstrated, that Cooper pairs can be separated, which opens the way for Einstein Podolsky Rosen pair generation and entanglement analysis of mobile electrons. On the other hand attaching F lead to a QD, ferromagnetism penetrates into the dot inducing a local exchange field. We have shown that this exchange field strongly depends on the charge state of the QD. Furthermore it can even change sign for the same state, which allows the spin reversal of the ground state of the QD by gate voltage. We have shown that such an F- quantum dot system act as an efficient spin current amplifier
Nanoscale spin-polarization in dilute magnetic semiconductor (In,Mn)Sb
Results of point contact Andreev reflection (PCAR) experiments on (In,Mn)Sb
are presented and analyzed in terms of current models of charge conversion at a
superconductor-ferromagnet interface. We investigate the influence of surface
transparency, and study the crossover from ballistic to diffusive transport
regime as contact size is varied. Application of a Nb tip to a (In,Mn)Sb sample
with Curie temperature Tc of 5.4 K allowed the determination of
spin-polarization when the ferromagnetic phase transition temperature is
crossed. We find a striking difference between the temperature dependence of
the local spin polarization and of the macroscopic magnetization, and
demonstrate that nanoscale clusters with magnetization close to the saturated
value are present even well above the magnetic phase transition temperature.Comment: 4 page
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