| 1. |
- Bylander, Jonas, 1978, et al.
(författare)
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Crossover from time-correlated single-electron tunneling to that of Cooper pairs
- 2007
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Ingår i: Physical Review B. - 2469-9969 .- 2469-9950. ; 76:2, s. 020506(R)-
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Tidskriftsartikel (refereegranskat)abstract
- We have studied charge transport in a one-dimensional chain of small Josephson junctions using a single-electron transistor. We observe a crossover from time-correlated tunneling of single electrons to that of Cooper pairs as a function of both magnetic field and current. At relatively high magnetic field, single-electron transport dominates and the tunneling frequency is given by f=I/e, where I is the current through the chain and e is the electron's charge. As the magnetic field is lowered, the frequency gradually shifts to f=I/2e for I>200 fA, indicating Cooper-pair transport. For the parameters of the measured sample, we expect the Cooper-pair transport to be incoherent.
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| 2. |
- Bylander, Jonas, 1978
(författare)
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Current measurement by real-time counting of single charges
- 2005
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The first real-time observation of time correlated single-electron tunnelling is reported in this thesis. This is a direct detection of charge discreteness in an electrical current.When a current, I, flows through a chain of metallic islands, connected by small tunnel junctions, a lattice of charges is formed due to the Coulomb repulsion. These charges propagate throughout the array by time correlated quantum mechanical tunnelling at the average frequency f=I/e, where e is the charge of the electron. This phenomenon is analogous to the AC Josephson effect.We have combined such a chain with an ultrasensitive charge sensor, a radio-frequency single-electron transistor (RF-SET), and injected the full charge into theSET island. By using the RF-SET to monitor the single charges as they pass by, we have measured currents in the range 5 fA1 pA by counting electrons. This is a fundamentally new way to measure small currents, which is more accurate than established techniques and moreover has the advantage of being self-calibrated since the only parameter involved is the natural constant e. As a consequence, the method does not suffer from measurement offset or drift. In an optimized device, with higher absolute current and better accuracy, we see a possibility to use our electron counter in an experiment that closes the quantum metrological triangle relating current, voltage and frequency by fundamental constants.Direct extensions of this work would be to look for Bloch oscillations of frequency f=I/2e in a superconducting array similar to the one used. Furthermore, our method could shed new light on the statistical properties of mesoscopic charge transport.
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| 3. |
- Bylander, Jonas, 1978, et al.
(författare)
-
Current measurement by real-time counting of single electrons
- 2005
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 434:7031, s. 361 - 364
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Tidskriftsartikel (refereegranskat)abstract
- The fact that electrical current is carried by individual charges has been known for over 100 years, yet this discreteness has not been directly observed so far. Almost all current measurements involve measuring the voltage drop across a resistor, using Ohm's law, in which the discrete nature of charge does not come into play. However, by sending a direct current through a microelectronic circuit with a chain of islands connected by small tunnel junctions, the individual electrons can be observed one by one. The quantum mechanical tunnelling of single charges in this one-dimensional array is time correlated, and consequently the detected signal has the average frequency f = I/e, where I is the current and e is the electron charge. Here we report a direct observation of these time-correlated single-electron tunnelling oscillations, and show electron counting in the range 5 fA1 pA. This represents a fundamentally new way to measure extremely small currents, without offset or drift. Moreover, our current measurement, which is based on electron counting, is self-calibrated, as the measured frequency is related to the current only by a natural constant.
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| 4. |
- Bylander, Jonas, 1978, et al.
(författare)
-
Direct observation of time correlated single-electron tunneling
- 2005
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Ingår i: Conference Program and Extended Abstracts. 10th International Superconductive Electronics Conference. ; , s. O-J.02
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We report a direct detection of time correlated single-electron tunneling oscillations in a series array of small tunnel junctions. Here the current, I, is made up of a lattice of charge solitons moving throughout the array by time correlated tunneling with the frequency f=I/e, where e is the electron charge. To detect the single charges, we have integrated the array with a radio-frequency single-electron transistor (RF-SET) and employed two different methods to couple the array to the SET input: by direct injection through a tunnel junction, and by capacitive coupling. In this paper we report the results from the latter type of charge input, where we have observed the oscillations in the frequency domain and measured currents from 50 to 250 fA by means of electron counting.
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| 5. |
- Bylander, Jonas, 1978, et al.
(författare)
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Line Widths of Single-Electron Tunneling Oscillations: Experiment and Numerical Simulations
- 2006
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Ingår i: AIP Conference Proceedings. 24th International Conference on Low Temperature Physics - LT24, Orlando, Florida (USA), 10-17 August 2005. Eds: Y. Takano, S. P. Hershfield, S. O. Hill, P. J. Hirschfeld, A. M. Goldman. - 0735403473 ; 850, s. 1442-1443
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Konferensbidrag (refereegranskat)
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| 6. |
- Bylander, Jonas, 1978, et al.
(författare)
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Pulse imaging and nonadiabatic control of solid-state artificial atoms
- 2009
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 80:22, s. 220506-
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Tidskriftsartikel (refereegranskat)abstract
- Transitions in an artificial atom, driven nonadiabatically through an energy-level avoided crossing, can be controlled by carefully engineering the driving protocol. We have driven a superconducting persistent-current qubit with a large-amplitude radio-frequency field. By applying a biharmonic wave form generated by a digital source, we demonstrate a mapping between the amplitude and phase of the harmonics produced at the source and those received by the device. This allows us to image the actual wave form at the device. This information is used to engineer a desired time dependence, as confirmed by the detailed comparison with a simulation. © 2009 The American Physical Society.
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| 7. |
- Bylander, Jonas, 1978
(författare)
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Time-resolved detection of temporally correlated, single-charge tunnelling
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- We report real-time detection of the single charges that constitute a small electrical current, as they flow through a nano-electronic device. This represents a direct demonstration of charge discreteness in an electrical current.In a chain of small metallic islands connected by tunnel junctions (allowing electrons to pass by quantum tunnelling), Coulomb repulsion imposes a spatial correlation between single electrons which occupy different islands. When a current I flows through this chain, these electrons move in concert, and tunnel in atemporally correlated way at the average frequency f_e=I/e, where e is the electronic charge. We have been able to detect this time-correlated, single-electron tunnelling by combining such a chain with an ultrasensitive charge detector, a radio-frequency single-electron transistor (RF-SET). Two different ways of connecting the chain to the SET were investigated. We ultimately measured currents in the range 5 fA-1 pA bycounting the single electrons. We found that the line width of the spectral peak is nearly proportional to the frequency f_e of the oscillations, in good agreement between experimental data and numerical calculations. The tunnelling of the single electrons took place while the islands were in the superconducting state, but the inter-island Josephson coupling was low. Cooper pairs were also easily broken into quasiparticles as the magnetic field was relatively strong. Under these conditions, we have additionally observed a crossover to time-correlated, incoherent tunnelling of individual Cooper pairs as a function of decreased magnetic field and of current. Tunnelling dominated by Cooper pairs now produces a frequency f_2e=I/2e. We have found that the two types of tunnelling can coexist in an intermediate state, producing an average tunnelling frequency between f_e and f_2e. In a similar way, we have also attempted to directly observe Bloch oscillations in a one-dimensional array of small Josephson junctions, that is, the coherent, time-correlated tunnelling of Cooper pairs. This fundamentally new way to measure small currents has the advantage of being self-calibrated, since the only parameter involved is the natural constant e. In an optimised device with higher current and better accuracy, we see a possibility to use our electron counter in metrological applications.
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