scholarly journals Cooper pair splitting in parallel quantum dot Josephson junctions

2015 ◽  
Vol 6 (1) ◽  
Author(s):  
R. S. Deacon ◽  
A. Oiwa ◽  
J. Sailer ◽  
S. Baba ◽  
Y. Kanai ◽  
...  
Keyword(s):  
Quantum Dot ◽  
Cooper Pair ◽  
Josephson Current ◽  
Cooper Pairs ◽  
Electron Pairs ◽  
On Demand ◽  
Non Local ◽  
Local Transport ◽  
Current Flows ◽  
A Current

Abstract 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.

scholarly journals Transport signatures of an Andreev molecule in a quantum dot–superconductor–quantum dot setup

2019 ◽  
Vol 10 ◽  
pp. 363-378 ◽  
Author(s):  
Zoltán Scherübl ◽  
András Pályi ◽  
Szabolcs Csonka
Keyword(s):  
Quantum Dots ◽  
Quantum Information ◽  
Quantum Dot ◽  
Cooper Pair ◽  
Differential Conductance ◽  
Zero Bias ◽  
Local Mechanism ◽  
Special Cases ◽  
Non Local ◽  
Hybrid Devices

Hybrid devices combining quantum dots with superconductors are important building blocks of conventional and topological quantum-information experiments. A requirement for the success of such experiments is to understand the various tunneling-induced non-local interaction mechanisms that are present in the devices, namely crossed Andreev reflection, elastic co-tunneling, and direct interdot tunneling. Here, we provide a theoretical study of a simple device that consists of two quantum dots and a superconductor tunnel-coupled to the dots, often called a Cooper-pair splitter. We study the three special cases where one of the three non-local mechanisms dominates, and calculate measurable ground-state properties, as well as the zero-bias and finite-bias differential conductance characterizing electron transport through this device. We describe how each non-local mechanism controls the measurable quantities, and thereby find experimental fingerprints that allow one to identify and quantify the dominant non-local mechanism using experimental data. Finally, we study the triplet blockade effect and the associated negative differential conductance in the Cooper-pair splitter, and show that they can arise regardless of the nature of the dominant non-local coupling mechanism. Our results should facilitate the characterization of hybrid devices, and their optimization for various quantum-information-related experiments and applications.

scholarly journals Thermoelectric current in a graphene Cooper pair splitter

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Z. B. Tan ◽  
A. Laitinen ◽  
N. S. Kirsanov ◽  
A. Galda ◽  
V. M. Vinokur ◽  
...  
Keyword(s):  
Cooper Pair ◽  
Theoretical Description ◽  
Seebeck Effect ◽  
Normal Metal ◽  
Electric Voltage ◽  
Power Generators ◽  
Metal Structures ◽  
Fundamental Phenomenon ◽  
Non Local ◽  
Cooper Pair Splitting

AbstractGeneration of electric voltage in a conductor by applying a temperature gradient is a fundamental phenomenon called the Seebeck effect. This effect and its inverse is widely exploited in diverse applications ranging from thermoelectric power generators to temperature sensing. Recently, a possibility of thermoelectricity arising from the interplay of the non-local Cooper pair splitting and the elastic co-tunneling in the hybrid normal metal-superconductor-normal metal structures was predicted. Here, we report the observation of the non-local Seebeck effect in a graphene-based Cooper pair splitting device comprising two quantum dots connected to an aluminum superconductor and present a theoretical description of this phenomenon. The observed non-local Seebeck effect offers an efficient tool for producing entangled electrons.

scholarly journals Multiplicity, Parity and Angular Momentum of a Cooper Pair in Unconventional Superconductors of D4h Symmetry: Sr2RuO4 and Fe-Pnictide Materials

Symmetry ◽  
2021 ◽  
Vol 13 (8) ◽  
pp. 1435
Author(s):  
Victor G. Yarzhemsky
Keyword(s):  
Angular Momentum ◽  
Cooper Pair ◽  
Point Group ◽  
Group Symmetry ◽  
Cooper Pairs ◽  
Group Approach ◽  
Angular Momentum Projection ◽  
Space Group ◽  
Unconventional Superconductors ◽  
Even Pairs

Sr2RuO4 and Fe-pnictide superconductors belong to the same point group symmetry D4h. Many experimental data confirm odd pairs in Sr2RuO4 and even pairs in Fe-pnictides, but opposite conclusions also exist. Recent NMR results of Pustogow et al., which revealed even Cooper pairs in Sr2RuO4, require reconsideration of symmetry treatment of its SOP (superconducting order parameter). In the present work making use of the Mackey–Bradley theorem on symmetrized squares, a group theoretical investigation of possible pairing states in D4h symmetry is performed. It is obtained for I4/mmm , i.e., space group of Sr2RuO4, that triplet pairs with even spatial parts are possible in kz direction and in points M and Y. For the two latter cases pairing of equivalent electrons with nonzero total momentum is proposed. In P4/nmm space group of Fe- pnictides in point M, even and odd pairs are possible for singlet and triplet cases. It it shown that even and odd chiral states with angular momentum projection m=±1 have nodes in vertical planes, but Eg is nodal , whereas Eu is nodeless in the basal plane. It is also shown that the widely accepted assertion that the parity of angular momentum value is directly connected with the spatial parity of a pair is not valid in a space-group approach to the wavefunction of a Cooper pair.

scholarly journals Sliding Contacts in Planetary Magnetospheres

Symmetry ◽  
2021 ◽  
Vol 13 (2) ◽  
pp. 283
Author(s):  
Elena Belenkaya ◽  
Igor Alexeev
Keyword(s):  
Large Scale ◽  
Strong Field ◽  
Magnetized Plasma ◽  
Sliding Contacts ◽  
Radio Emissions ◽  
Planetary Magnetospheres ◽  
Current Task ◽  
Surrounding Space ◽  
Non Local ◽  
A Current

In the planetary magnetospheres there are specific places connected with velocity breakdown, reconnection, and dynamo processes. Here we pay attention to sliding layers. Sliding layers are formed in the ionosphere, on separatrix surfaces, at the magnetopauses and boundaries of stellar astrospheres, and at the Alfvén radius in the equatorial magnetosphere of rapidly rotating strongly magnetized giant planets. Although sliding contacts usually occur in thin local layers, their influence on the global structure of the surrounding space is very great. Therefore, they are associated with non-local processes that play a key role on a large scale. There can be an exchange between different forms of energy, a generation of strong field-aligned currents and emissions, and an amplification of magnetic fields. Depending on the conditions in the magnetosphere of the planet/exoplanet and in the flow of magnetized plasma passing it, different numbers of sliding layers with different configurations appear. Some are associated with regions of auroras and possible radio emissions. The search for planetary radio emissions is a current task in the detection of exoplanets.

scholarly journals On-demand thermoelectric generation of equal-spin Cooper pairs

2020 ◽  
Vol 2 (2) ◽  
Author(s):  
Felix Keidel ◽  
Sun-Yong Hwang ◽  
Björn Trauzettel ◽  
Björn Sothmann ◽  
Pablo Burset
Keyword(s):  
Cooper Pairs ◽  
Thermoelectric Generation ◽  
On Demand

scholarly journals Voltage staircase in a current-biased quantum-dot Josephson junction

2021 ◽  
Vol 103 (9) ◽  
Author(s):  
D. O. Oriekhov ◽  
Y. Cheipesh ◽  
C. W. J. Beenakker
Keyword(s):  
Quantum Dot ◽  
Josephson Junction ◽  
A Current

scholarly journals Superconducting coherence length of hole-doped cuprates obtained from electron–boson spectral density function

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Jungseek Hwang
Keyword(s):  
Spectral Density ◽  
Coherence Length ◽  
Cooper Pair ◽  
Average Frequency ◽  
Spin Fluctuations ◽  
Fermi Velocity ◽  
Cooper Pairs ◽  
Spectroscopic Techniques ◽  
Microscopic Mechanism ◽  
Superconducting Coherence Length

AbstractElectron–boson spectral density functions (EBSDFs) can be obtained from measured spectra using various spectroscopic techniques, including optical spectroscopy. EBSDFs, known as glue functions, are suggested to have a magnetic origin. Here, we investigated EBSDFs obtained from the measured optical spectra of hole-doped cuprates with wide doping levels, from underdoped to overdoped cuprates. The average frequency of an EBSDF provides the timescale for the spin fluctuations to form Cooper pairs. This timescale is directly associated with retarded interactions between electrons. Using this timescale and Fermi velocity, a reasonable superconducting coherence length, which reflects the size of the Cooper pair, can be extracted. The obtained coherence lengths were consistent with those measured via other experimental techniques. Therefore, the formation of Cooper pairs in cuprates can be explained by spin fluctuations, the timescales of which appear in EBSDFs. Consequently, EBSDFs provide crucial information on the timescale of the microscopic mechanism of Cooper pair formation.

scholarly journals Understanding the Josephson Current through a Kondo-Correlated Quantum Dot

2012 ◽  
Vol 108 (22) ◽  
Author(s):  
D. J. Luitz ◽  
F. F. Assaad ◽  
T. Novotný ◽  
C. Karrasch ◽  
V. Meden
Keyword(s):  
Quantum Dot ◽  
Josephson Current

Universal quantum computation with quantum-dot cellular automata in decoherence-free subspace

2008 ◽  
Vol 8 (10) ◽  
pp. 977-985
Author(s):  
Z.-Y. Xu ◽  
M. Feng ◽  
W.-M. Zhang
Keyword(s):  
Cellular Automata ◽  
Quantum Dot ◽  
Quantum Computation ◽  
Two Dimensions ◽  
High Fidelity ◽  
Electron Pairs ◽  
Quantum Dot Cellular Automata ◽  
Single Spin ◽  
Universal Quantum ◽  
Decoherence Free Subspace

We investigate the possibility to have electron-pairs in decoherence-free subspace (DFS), by means of the quantum-dot cellular automata (QCA) and single-spin rotations, to deterministically carry out a universal quantum computation with high-fidelity. We show that our QCA device with electrons tunneling in two dimensions is very suitable for DFS encoding, and argue that our design favors a scalable quantum computation robust to collective dephasing errors.

Sign in / Sign up

Export Citation Format

Share Document