Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Pulse and hold switching current readout of superconducting quantum circuits
KTH, School of Engineering Sciences (SCI), Physics.
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Josephson junction qubits are promising candidates for a scalable quantum processor. Such qubits are commonly manipulated by means of sequences of rf-pulses and different methods are used to determine their quantum state. The readout should be able to distinguish the two qubit states with high accuracy and be faster than the relaxation time of the qubit. We discuss and experiment with a readout method based on the switching of a Josephson junction from the zero voltage state to a finite voltage state.

The Josephson junction circuit has a non-linear dynamics and when it is brought to a bifurcation point, it can be made arbitrarily sensitive to small perturbations. This extreme sensitivity at a bifurcation point can be used to distinguish the two quantum states if the topology of the phase space of the circuit leads to a quick separation into the final states where re-crossings of the bifurcation point are negligible. We optimize a switching current detector by analyzing the phase space of a Josephson junction circuit with frequency dependent damping.

A pulse and hold technique is used where an initial current pulse brings the junction close to its bifurcation point and the subsequent hold level is used to give the circuit enough time to evolve until the two states can be distinguished by the measuring instrument. We generate the pulse and hold waveform by a new technique where a voltage step with following linear voltage rise is applied to a bias capacitor. The frequency dependent damping is realized by an on-chip RC-environment fabricated with optical lithography. Josephson junction circuits are added on by means of e-beam lithography.

Measurements show that switching currents can be detected with pulses as short as 5 ns and a resolution of 2.5% for a sample directly connected to the measurement leads of the cryostat. Detailed analysis of the switching currents in the RC-environment show that pulses with a duration of 20 us can be explained by a generalization of Kramers' escape theory, whereas switching the same sample with 25 ns pulses occurs out of thermal equilibrium, with sensitivity and speed adequate for qubit readout.

Place, publisher, year, edition, pages
Stockholm: KTH , 2006. , viii, 82 p.
Series
Trita-FYS, ISSN 0280-316X ; 2006:61
Keyword [en]
Josephson junction, readout, qubit, detector, frequency dependent damping, quantronium, phase-space, correlation analysis
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-4156ISBN: 91-7178-462-4 (print)OAI: oai:DiVA.org:kth-4156DiVA: diva2:10954
Public defence
2006-11-10, FA32, AlbaNova Main Building, Roslagstullsbacken 21, Stockholm, 13:00
Opponent
Supervisors
Note
QC 20100924Available from: 2006-10-23 Created: 2006-10-23 Last updated: 2010-09-24Bibliographically approved
List of papers
1. Pulse and Hold Strategy for Switching Current Measurements
Open this publication in new window or tab >>Pulse and Hold Strategy for Switching Current Measurements
2007 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 75, no 9, 094515- p.Article in journal (Refereed) Published
Abstract [en]

We investigate by theory and experiment, the Josephson junction switching current detector in an environment with frequency-dependent damping. Analysis of the circuit's phase space shows that a favorable topology for switching can be obtained with overdamped dynamics at high frequencies. A pulse-and-hold method is described, where a fast switch pulse brings the circuit close to an unstable point in the phase space when biased at the hold level. Experiments are performed on Cooper pair transistors and quantronium circuits, which are overdamped at high frequencies with an on-chip RC shunt. For 20 mu s switch pulses the switching process is well described by thermal equilibrium escape, based on a generalization of the Kramers formula to the case of frequency-dependent damping. A capacitor bias method is used to create very rapid, 25 ns switch pulses, where it is observed that the switching process is not governed by thermal equilibrium noise.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-6275 (URN)10.1103/PhysRevB.75.094515 (DOI)000245328500089 ()2-s2.0-34047190361 (Scopus ID)
Note
QC 20100812Available from: 2006-10-23 Created: 2006-10-23 Last updated: 2011-11-07Bibliographically approved
2. Phase Space Topology of a Switching Current Detector
Open this publication in new window or tab >>Phase Space Topology of a Switching Current Detector
Show others...
2006 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 73, 132511- p.Article in journal (Refereed) Published
Abstract [en]

We examine in theory and by numerical simulation, the dynamic process of switching from a zero voltage to a finite voltage state in a Josephson junction circuit. The theoretical model describes small capacitance Josephson junctions which are overdamped at high frequencies, and can be applied to detection of the quantum state of a qubit circuit. We show that the speed and fidelity of the readout are strongly influenced by the topology of the phase space attractors. The readout will be close to optimal when choosing the circuit parameters so as to avoid having an unstable limiting cycle which separates the two basins of attraction.

Keyword
josephson-junctions; quantum-state
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-6276 (URN)10.1103/PhysRevB.73.132511 (DOI)000237153800028 ()2-s2.0-33646232997 (Scopus ID)
Note
QC 20100812Available from: 2006-10-23 Created: 2006-10-23 Last updated: 2010-09-24Bibliographically approved
3. Time Domain Analysis of Dynamical Switching in a Josephson Junction
Open this publication in new window or tab >>Time Domain Analysis of Dynamical Switching in a Josephson Junction
Show others...
2004 (English)Manuscript (preprint) (Other academic)
Abstract [en]

We have studied the switching behaviour of a small capacitance Josephson junction both in experiment,and by numerical simulation of a model circuit. The switching is a complex process involvingthe transition between two dynamical states of the non-linear circuit, arising from a frequency dependentdamping of the Josephson junction. We show how a specific type of bias pulse-and-hold,can result in a fast detection of switching, even when the measurement bandwidth of the junctionvoltage is severely limited, and/or the level of the switching current is rather low.

National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-6277 (URN)
Note

QC 20100924

Available from: 2006-10-23 Created: 2006-10-23 Last updated: 2014-10-29Bibliographically approved
4. Fast Switching Current Detection at low Critical Currents
Open this publication in new window or tab >>Fast Switching Current Detection at low Critical Currents
2005 (English)In: Realizing Controllable Quantum States - MESOSCOPIC SUPERCONDUCTIVITY AND SPINTRONICS, 2005, 255-262 p.Conference paper, Published paper (Refereed)
Abstract [en]

A pulse-and-hold technique is used to measure the switching of small critical current Josephson junctions. This technique allows one to achieve a good binary detection and therefore measure switching probabilities. The technique overcomes limitations on simple square pulses and allows for the measurement of junctions with critical currents of the order of 10nA with bias pulses of the order of 100ns. A correlation analysis of the switching events is performed to show how the switching probability depends on the wait time between repeated bias pulses.

Keyword
tunnel-junctions, circuit, state
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-6278 (URN)000234363700039 ()981-256-468-3 (ISBN)
Conference
3rd International Symposium on Mesoscopic Superconductivity and Spintronics Atsugi City, JAPAN, MAR 01-04, 2004
Note
QC 20100924Available from: 2006-10-23 Created: 2006-10-23 Last updated: 2010-09-28Bibliographically approved
5. Switching Current of a Cooper Pair Transistor with Tunable Josephson Junctions
Open this publication in new window or tab >>Switching Current of a Cooper Pair Transistor with Tunable Josephson Junctions
2002 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 66, no 1, 14510- p.Article in journal (Refereed) Published
Abstract [en]

We investigate the switching current of a Cooper pair transistor with tunable Josephson energy. The junctions are fabricated in a superconducting quantum interference device (SQUID) geometry which allows for an in situ tunable effective Josephson energy by application of a magnetic field. We find a 2e-periodic switching current versus gate charge. As the magnetic field is increased the switching current stays 2e-periodic but the magnitude is suppressed. At a magnetic field of half a flux quantum through the SQUID's the switching current is minimum. We can theoretically model the experimental data by assuming a switching current which is proportional to the ideal critical current squarred. We show that such a dependence is expected in the limit where the effect of thermal fluctuations on the system is strong.

Keyword
single-electron transistor, bloch transistors, periodicity, 2e
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-6279 (URN)10.1103/PhysRevB.66.014510 (DOI)000177284900124 ()
Note
QC 20100924Available from: 2006-10-23 Created: 2006-10-23 Last updated: 2010-09-24Bibliographically approved
6. Switching Currents and Quasi-Particle Poisoning in the Superconducting Single Electron Transistor
Open this publication in new window or tab >>Switching Currents and Quasi-Particle Poisoning in the Superconducting Single Electron Transistor
2002 (English)In: INTERNATIONAL WORKSHOP ON SUPERCONDUCTING NANO-ELECTRONICS DEVICES, 2002, 25-31 p.Conference paper, Published paper (Refereed)
Keyword
parity-induced suppression, bloch transistors, coulomb-blockade, josephson, periodicity, junctions, behavior, 2e
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-6280 (URN)000181696000004 ()0-306-47266-X (ISBN)
Conference
International Workshop on Superconducting Nano-Electronics Devices NAPLES, ITALY, MAY 28-JUN 01, 2001
Note
QC 20100924Available from: 2006-10-23 Created: 2006-10-23 Last updated: 2010-09-24Bibliographically approved

Open Access in DiVA

fulltext(3029 kB)492 downloads
File information
File name FULLTEXT01.pdfFile size 3029 kBChecksum MD5
7eddd6ead0f42330703f9e7a7f019b0cac9a2ee3150c9fd23c326afaf76a7595f8fb1520
Type fulltextMimetype application/pdf

Search in DiVA

By author/editor
Walter, Jochen
By organisation
Physics
Physical Sciences

Search outside of DiVA

GoogleGoogle Scholar
Total: 492 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 464 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf