Devices to generate on-demand non-local spin entangled electron pairs have potential application as solid-state analogues of the entangled photon sources used in quantum optics. Recently, Andreev entanglers that use two quantum dots as filters to adiabatically split and separate the quasi-particles of Cooper pairs have shown efficient splitting through measurements of the transport charge but the spin entanglement has not been directly confirmed. Here we report measurements on parallel quantum dot Josephson junction devices allowing a Josephson current to flow due to the adiabatic splitting and recombination of the Cooper pair between the dots. The evidence for this non-local transport is confirmed through study of the non-dissipative supercurrent while tuning independently the dots with local electrical gates. As the Josephson current arises only from processes that maintain the coherence, we can confirm that a current flows from the spatially separated entangled pair.

We present a systematical experimental investigation of an unusual transport phenomenon observed in two dimensional electron gases in Si/SiGe heterostructures under integer quantum Hall effect (IQHE) conditions. This phenomenon emerges under specific experimental conditions and in different material systems. It is commonly referred to as Hall resistance overshoot, however, lacks a consistent explanation so far. Based on our experimental findings we are able to develop a model that accounts for all of our observations in the framework of a screening theory for the IQHE. Within this model the origin of the overshoot is attributed to a transport regime where current is confined to co-existing evanescent incompressible strips of different filling factors.

We present a few electron double quantum dot device defined in an isotopically purified 28 Si quantum well (QW). An electron mobility of 5.5 · 10 4 cm 2 (Vs) −1 is observed in the QW which is the highest mobility ever reported for a two-dimensional electron system in 28 Si. The residual concentration of 29 Si nuclei in the 28 Si QW is lower than 10 3 ppm, at the verge where the hyperfine interaction is theoretically no longer expected to dominantly limit the T 2 spin dephasing time. We also demonstrate a complete suppression of hysteretic gate behavior and charge noise using a negatively biased global top gate.PACS numbers: 73.63. Kv, 73.23.Hk, 73.21.Fg, 28.60.+s, 72.70.+m, 73.50.Td Semiconductor quantum dots (QD) are among the candidates for a scalable implementation of electron spin based qubits in solid state systems. Silicon (Si) has been widely recognized as a well suited material system for decoupling electron spin qubits from their volatile solid state environment owing to the weak spin-orbit and weak hyperfine interaction. Very long spin relaxation times (T 1 ) on the order of seconds have been reported for Si on the basis of electrostatically defined QDs 1 , single phosphorous donors 2 or triplet-singlet relaxation times in double QDs 3 . Recently, also a spin dephasing time of T * 2 = 360 ns has been observed in a time ensemble measurement in a Si double QD 4 . These milestones highlight the great potential for quantum information processing in Si.The adverse impact from nuclear spins on electron spin coherence 5 can be further reduced in the Si material system by means of isotopic enrichment of the 28 Si isotope which has zero nuclear spin. Recent technological advances have enabled the fabrication of highly enriched 28 Si crystals 6 with isotopic fractions of the nuclear spin carrying 29 Si isotope smaller than 4 · 10 2 ppm. In such ultra-clean 28 Si bulk samples, the spin coherence time T 2 for donor-bound electrons 7 achieves unprecedentedly long values of T 2 = 10 s. This offers a promising perspective for qubit applications with electrostatically defined QDs in 28 Si heterostructures. However, the integration of isotopically purified material with low impurity concentrations into molecular beam epitaxy (MBE) or chemical vapor deposition growth processes is still a challenge. Hence, no QD devices have been demonstrated so far for two-dimensional electron systems (2DES) in 28 Si.In this letter, we report on the fabrication and characterization of an electrostatically defined few electron double QD within a high mobility 2DES in a MBEgrown 28 Si/SiGe heterostructure. We find a concentration of residual 29 Si nuclei in the quantum well (QW) smaller than 10 3 ppm and achieve a peak mobility of 5.5 · 10 4 cm 2 (Vs) −1 at a 2DES density of 3 · 10 11 cm −2 . We combine our double QD with a global top gate (TG) and demonstrate a strong suppression of hysteretic gate behavior and charge noise as a negative voltage is applied to the global TG.Our heterostructures are grown in a solid source MBE system equ...