| 1. |
- Ergül, Adem, et al.
(författare)
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Localizing quantum phase slips in one-dimensional Josephson junction chains
- 2013
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 15, s. 095014-
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Tidskriftsartikel (refereegranskat)abstract
- We studied quantum phase-slip (QPS) phenomena in long one-dimensional Josephson junction series arrays with tunable Josephson coupling. These chains were fabricated with as many as 2888 junctions, where one sample had a separately tunable link in the middle of the chain. Measurements were made of the zero-bias resistance, R-0, as well as current-voltage characteristics (IVC). The finite R-0 is explained by QPS and shows an exponential dependence on root E-J/E-C with a distinct change in the exponent at R-0 = R-Q = h/4e(2). When R-0 > R-Q, the IVC clearly shows a remnant of the Coulomb blockade, which evolves to a zero-current state with a sharp critical voltage as E-J is tuned to a smaller value. The zero-current state below the critical voltage is due to coherent QPSs and we show that these are enhanced when the central link is weaker than all other links. Above the critical voltage, a negative, differential resistance is observed, which nearly restores the zero-current state.
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| 2. |
- Ergül, Adem, et al.
(författare)
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Phase sticking in one-dimensional Josephson junction chains
- 2013
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 88:10, s. 104501-
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Tidskriftsartikel (refereegranskat)abstract
- We studied current-voltage characteristics of long one-dimensional Josephson junction chains with Josephson energy much larger than charging energy, E-J >> E-C. In this regime, typical I-V curves of the samples consist of a supercurrent-like branch at low-bias voltages followed by a voltage-independent chain current branch, I-chain at high bias. Our experiments showed that I-chain is not only voltage-independent but it is also practically temperature-independent up to T = 0.7T(C). We have successfully model the transport properties in these chains using a capacitively shunted junction model with nonlinear damping.
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| 3. |
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| 4. |
- Tholén, E., et al.
(författare)
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Gain, noise and intermodulation in a nonlinear superconducting resonator
- 2014
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Ingår i: EPJ Quantum Technology. - : SpringerOpen. - 2196-0763. ; 1:1
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Tidskriftsartikel (refereegranskat)abstract
- A superconducting microwave resonator is modified with several weak links to make it nonlinear and operated as a phase-insensitive microwave amplifier. Signal gain is demonstrated by intermodulation with a strong pump. The gain is sharply frequency dependent, and we demonstrate phase dependence by examining correlations between the signal and one idler which is a 3rd order intermodulation product of the pump and signal tones. A calibration procedure is described which is based on measurement of both thermal and quantum noise, revealing that the following HEMT amplifier adds noise at 15 times the quantum limit. When operated as a phase-insensitive amplifier the nonlinear resonator added noise at 2.5 times the quantum limit. Significant power is found at intermodulation products beyond 3rd order, which may be responsible for the inability to reach the quantum limit
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| 5. |
- Agren, P., et al.
(författare)
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Hysteretic current-voltage characteristics and Coulomb blockade in 1D-arrays of Josephson junctions
- 2000
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Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 280:04-jan, s. 414-415
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Tidskriftsartikel (refereegranskat)abstract
- The IV characteristics (IVC) of 1D-arrays of small capacitance Josephson junctions with E-C similar to E-J have been measured. The IVC show Coulomb blockade of Cooper pair tunneling and exhibit a pronounced hysteresis which appears to be dual to the well-known resistively shunted junction behavior of ordinary Josephson junctions. A dual serially resistive junction model is used to qualitatively explain the measured data.
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| 6. |
- Agren, P., et al.
(författare)
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Kinetic inductance and Coulomb blockade in one dimensional Josephson junction arrays
- 2001
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Ingår i: Journal of Low Temperature Physics. - 0022-2291 .- 1573-7357. ; 124:02-jan, s. 291-304
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Tidskriftsartikel (refereegranskat)abstract
- One dimensional Josephson junction arrays have been fabricated and current-voltage characteristics (IVC) have been measured at cryogenic temperatures. The arrays were fabricated in a SQUID-geometry which allowed an in. situ tuning of thc Josephson energy by application of a magnetic field. The IVC of thc arrays shows a clear Coulomb blockade state. In the Coulomb blockade regime the IVC are hysteretic, The array is modeled using a Serial resistive-inductive-junction model which is able to qualitatively explain the IVC. In this model an inductance of the order of 0.1-10 mH per Junction is needed to account for the hysteresis. Kinetic inductance. stemming from the inertia of the Cooper pairs. gives the correct order of magnitude. The problem of self-heating is also discussed as an alternative explanation of the hysteresis.
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| 7. |
- Andersson, Gustav, et al.
(författare)
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Squeezing and Multimode Entanglement of Surface Acoustic Wave Phonons
- 2022
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Ingår i: PRX Quantum. - : American Physical Society (APS). - 2691-3399. ; 3:1
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Tidskriftsartikel (refereegranskat)abstract
- Exploiting multiple modes in a quantum acoustic device could enable applications in quantum information in a hardware-efficient setup, including quantum simulation in a synthetic dimension and continuous-variable quantum computing with cluster states. We develop a multimode surface acoustic wave (SAW) resonator with a superconducting quantum interference device (SQUID) integrated in one of the Bragg reflectors. The interaction with the SQUID-shunted mirror gives rise to coupling between the more than 20 accessible resonator modes. We exploit this coupling to demonstrate two-mode squeezing of SAW phonons, as well as four-mode multipartite entanglement. Our results open avenues for continuous-variable quantum computing in a compact hybrid quantum system.
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| 8. |
- Andersson, K., et al.
(författare)
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Escape from a zero-current state in a one-dimensional array of Josephson junctions
- 2003
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 67:9
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Tidskriftsartikel (refereegranskat)abstract
- A long one-dimensional array of small Josephson junctions exhibits Coulomb blockade of Cooper pair tunneling. This zero-current state exists up to a switching voltage, V-sw, where there is a sudden onset of current. In this paper we present histograms showing how V-sw changes with temperature for a long array and calculations of the corresponding escape rates. Our analysis of the problem is based on the existence of a voltage-dependent energy barrier and we do not make any assumptions about its shape. The data divide into two temperature regimes, the higher of which can be explained with the Kramers thermal escape model. At low temperatures the escape becomes independent of temperature.
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| 9. |
- Andersson, K., et al.
(författare)
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Synchronous Cooper pair tunneling in a 1D-array of Josephson junctions
- 2000
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Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 284, s. 1816-1817
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Tidskriftsartikel (refereegranskat)abstract
- We have studied 1D-arrays of Josephson junctions with a gate capacitively coupled to the middle of the array. The SQUID shape of each junction enables tuning of the Josephson coupling energy, El. By adding a signal to the gate with a radio-frequency f we create a step in the I-V characteristics at the value I = 2ef: The step is clearly visible as a peak in the differential resistance dI/dV and can be seen in the whole frequency range studied (10-90 MHz).
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| 10. |
- Arvidsson, Elisabet, et al.
(författare)
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Sensing force gradients with cavity optomechanics while evading backaction
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We study force gradient sensing by a coherently driven mechanical resonator with phase-sensitive detection of motion via the two-tone backaction evading measurement of cavity optomechanics. The response of the cavity to two coherent pumps is solved by numerical integration of the classical equations of motion, showing an extended region of monotonic response. We use Floquet theory to model the fluctuations, which rise only slightly above that of the usual backaction evading measurement in the presence of the mechanical drive. Our analysis indicates that this sensing technique is advantageous for applications such as Atomic Force Microscopy.
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