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NbTiN for improved superconducting detectors
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics. (Quantum Nano Photonics)ORCID iD: 0000-0003-1831-2208
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The physics of single photons is fascinating, by manipulating them we can observe and probe quantum effects. Doing so requires the fabrication and utilization of single photon sources, of which many types have been developed including quantum dots, trapped atoms and ions, and color centers. On the other end of the experiments, single photon detectors play a role of utmost importance, and while several types of detectors exist, superconducting nanowire single photon detectors are now the state-of-the-art technology. By offering near unity detection efficiency from the ultra-violet to the mid-infrared light spectrum, with negligible noise and excellent time resolution, they made possible many experiments that were previously technologically unfeasible. The same appealing characteristics have found a use in applications outside of the quantum optics framework, with notably light detection and ranging, biomedical imaging or CMOS circuits testing.In this thesis a controlled growth method for tailoring the characteristics of niobium titanium nitride in the framework of superconducting nanowire single photon detectors was developed. Reactive co-sputter deposition of niobium titanium nitride was shown to be a versatile method, both in terms of the degree of control over the material composition, and in the choice of substrates that it allows. Unity internal detection efficiency of detectors at telecom wavelengths was achieved by optimizing the niobium content in the material. The influence of lattice matching on the critical temperatures of films deposited at room temperature was investigated. The fabrication of superconducting nanowire single photon detectors on aluminum nitride-on-sapphire, on lithium niobate nano-waveguides, on gallium arsenide, and the integration on SiN waveguides was achieved. The material was used to fabricate detectors with optimized response for any linear polarization of the incoming photons by using a fractal architecture. Another method was proposed to achieve the same results by encapsulating meandering detectors in a high index dielectric material, resulting in a decrease of the permittivity mismatch between the nanowire material and its surrounding and therefore optimizing the efficiency for both orthogonal linear polarizations.Finally, detectors were fabricated from films developed in this work, and were operated to enable the implementation of polarization-based entanglement distribution in optical fibers in a real-conditions scenario, over a record distance of 96 km. This paves the way for the development of quantum communication networks using existing optical fiber links.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2019. , p. iii-xviii, 66
Series
TRITA-SCI-GRU ; 2019:34
Keywords [en]
superconducting nanowire sngle photon detector, SNSPD, niobium titanium nitride, NbTiN, reactive co-sputtering, quantum communications, quantum sensing
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
URN: urn:nbn:se:kth:diva-251759ISBN: 978-91-7873-192-3 (print)OAI: oai:DiVA.org:kth-251759DiVA, id: diva2:1316907
Public defence
2019-06-14, FB42, Roslagstullbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
EU, European Research Council, 307687Swedish Research Council, 638-2013-7152
Note

QC 20190521

Available from: 2019-05-21 Created: 2019-05-21 Last updated: 2019-05-22Bibliographically approved
List of papers
1. NbxTi1-xN low timing jitter single-photon detectors with unity internal detection efficiency at 1550 nm
Open this publication in new window or tab >>NbxTi1-xN low timing jitter single-photon detectors with unity internal detection efficiency at 1550 nm
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

The requirements in quantum optics experiments for high single photon detectionefficiency, low timing jitter, low dark count rate and short dead time have been fulfilled withthe development of superconducting nanowire single photon detectors. Although they offer adetection efficiency above 90%, achieving a high time resolution in devices made ofamorphous materials is a challenge, particularly at temperatures above 0.8 K. Devices madefrom niobium nitride and niobium titanium nitride allow to reach the best timing jitter, but inturn have stronger requirements in terms of film quality to achieve a high efficiency. Here wetake advantage of the flexibility of reactive co-sputter deposition to tailor the composition ofNbxTi1-xN superconducting films, and show that a Nb fraction of x = 0.62 allows for thefabrication of detectors from films as thick as 9 nm and covering an active area of 20 μm,with a wide detection saturation plateau at telecom wavelengths and in particular at 1550 nm.This is a signature of an internal detection efficiency saturation, achieved while maintainingthe high time resolution associated with NbTiN and operation at 2.5K. With our optimizedrecipe, we reliably fabricated detectors with high critical current densities reaching asaturation plateau at 1550 nm with 80% system detection efficiency, and with a FWHMtiming jitter as low as 19.47 ps.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-251747 (URN)
Funder
Swedish Research Council, 2013-7152Knut and Alice Wallenberg Foundation
Note

QC 20190521

Available from: 2019-05-21 Created: 2019-05-21 Last updated: 2019-05-21Bibliographically approved
2. Improvement of the critical temperature of NbTiN films on III-nitride substrates
Open this publication in new window or tab >>Improvement of the critical temperature of NbTiN films on III-nitride substrates
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2019 (English)In: Superconductors Science and Technology, ISSN 0953-2048, E-ISSN 1361-6668, Vol. 32, no 3, article id 035008Article in journal (Refereed) Published
Abstract [en]

In this paper, we study the impact of using III-nitride semiconductors (GaN, AlN) as substrates for ultrathin (11 nm) superconducting films of NbTiN deposited by reactive magnetron sputtering. The resulting NbTiN layers are (111)-oriented, fully relaxed, and they keep an epitaxial relation with the substrate. The higher critical superconducting temperature (T-c = 11.8 K) was obtained on AIN-on-sapphire, which was the substrate with smaller lattice mismatch with NbTiN. We attribute this improvement to a reduction of the NbTiN roughness, which appears associated with the relaxation of the lattice misfit with the substrate. On AlN-on-sapphire, superconducting nanowire single photon detectors were fabricated and tested, obtaining external quantum efficiencies that are in excellent agreement with theoretical calculations.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2019
Keywords
NbTiN, superconductor, GaN, AlN, single photon detector
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-244483 (URN)10.1088/1361-6668/aaf99d (DOI)000458129800001 ()2-s2.0-85062473569 (Scopus ID)
Note

QC 20190321

Available from: 2019-03-21 Created: 2019-03-21 Last updated: 2019-05-21Bibliographically approved
3. Heterogeneous integration of NbTiN by universal room temperature deposition
Open this publication in new window or tab >>Heterogeneous integration of NbTiN by universal room temperature deposition
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Being the Nb-based compound with the highest known critical temperature, NbTiN is of particular interest for many applications. It is used in Josephson junctions for single flux quantum logic gates, as a superconducting electrode to contact semiconductor devices, and one important use is in superconducting nanowire single photon detectors. These detectors are the ideal candidate for on-chip integration in photonic circuits, offering near-unity detection efficiency, low noise and excellent time resolution, therefore it is desirable to implement them on a wide variety of platforms. However, it remains a challenge to deposit the superconducting material with a process suitable for heterogeneous integration, as the most widespread material, NbN, is associated with a deposition at a high temperature. Taking advantage of the possibility to deposit superconducting NbTiN with various stoichiometries by co-sputter deposition at room temperature, we demonstrate growth on six different substrates – silicon dioxide, silicon nitride, gallium arsenide, lithium niobate, [Pb(Mg1/3Nb2/3)O3]-x[PbTiO3] or PMN-PT, and aluminum nitride – in the same deposition run, and show that all the films exhibit superconducting properties with similar critical temperatures. We fabricated waveguide-compatible superconducting nanowire single photon detectors on five substrates, report short dead times for all devices with a narrow spread of performances, and discuss their different photon detection saturation behavior. Our method simplifies the fabrication of superconducting devices on a wide range of materials.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-251751 (URN)
Note

QC 20190521

Available from: 2019-05-21 Created: 2019-05-21 Last updated: 2019-05-21Bibliographically approved
4. An NbTiN superconducting single photon detector implemented on a LiNbO3 nano-waveguide at telecom wavelength
Open this publication in new window or tab >>An NbTiN superconducting single photon detector implemented on a LiNbO3 nano-waveguide at telecom wavelength
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2019 (English)In: Poster session T.Po2, 2019Conference paper, Poster (with or without abstract) (Refereed)
Abstract [en]

Fiber-coupled superconducting nanowire single photon detectors are a ubiquitous tool for quantum optics experiments as they offer near unity detection efficiency over a broad wavelength range, low dark count rate, excellent time resolution and high saturation rate. Nevertheless, advancing quantum optics experiments and applications beyond the few-photon limit requires large scale integrated systems of quantum sources and detectors. In recent years there has been a tremendous progress with integrating single photon detectors with a variety of photonic platforms. This includes attempts on ion-diffused waveguides in LiNbO3, a non-linear and electro-optic material with widespread use for signal processing, frequency conversion, and quantum optics devices. However the realization of superconducting detectors on single mode waveguides remains elusive. Here we present an NbTiN superconducting single photon detector integrated directly on a LiNbO3 single mode nanophotonic waveguide at telecom wavelength, with a high critical current density and a dark count rate of 3 mHz at 99% of its critical current.

Keywords
SNSPD, lithium niobate
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-251754 (URN)
Conference
ECIO Conference in Ghent 2019
Funder
Swedish Research Council, 875994EU, European Research Council, ERC-2012-StGSwedish Research Council, 2013-7152Swedish Research Council, 2018-04487Swedish Research Council, 2016-03905
Note

QC 20190523

Available from: 2019-05-21 Created: 2019-05-21 Last updated: 2019-05-23Bibliographically approved
5. Controlled integration of selected detectors and emitters in photonic integrated circuits
Open this publication in new window or tab >>Controlled integration of selected detectors and emitters in photonic integrated circuits
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2019 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 27, no 3, p. 3710-3716Article in journal (Refereed) Published
Abstract [en]

Integration of superconducting nanowire single-photon detectors and quantum sources with photonic waveguides is crucial for realizing advanced quantum integrated circuits. However, scalability is hindered by stringent requirements on high-performance detectors. Here we overcome the yield limitation by controlled coupling of photonic channels to pre-selected detectors based on measuring critical current, timing resolution, and detection efficiency. As a proof of concept of our approach, we demonstrate a hybrid on-chip full-transceiver consisting of a deterministically integrated detector coupled to a selected nanowire quantum dot through a filtering circuit made of a silicon nitride waveguide and a ring resonator filter, delivering 100 dB suppression of the excitation laser. In addition, we perform extensive testing of the detectors before and after integration in the photonic circuit and show that the high performance of the superconducting nanowire detectors, including timing jitter down to 23 +/- 3 ps, is maintained. Our approach is fully compatible with wafer-level automated testing in a cleanroom environment. 

Place, publisher, year, edition, pages
OPTICAL SOC AMER, 2019
National Category
Accelerator Physics and Instrumentation
Identifiers
urn:nbn:se:kth:diva-244523 (URN)10.1364/OE.27.003710 (DOI)000457585600163 ()30732386 (PubMedID)2-s2.0-85061015801 (Scopus ID)
Note

QC 20190403

Available from: 2019-04-03 Created: 2019-04-03 Last updated: 2019-05-21Bibliographically approved
6. Polarization-insensitive fiber-coupled superconducting-nanowire single photon detector using a high-index dielectric capping layer
Open this publication in new window or tab >>Polarization-insensitive fiber-coupled superconducting-nanowire single photon detector using a high-index dielectric capping layer
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2018 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 26, no 13, p. 17697-17704Article in journal (Refereed) Published
Abstract [en]

Superconducting-nanowire single photon detectors (SNSPDs) are able to reach near-unity detection efficiency in the infrared spectral range. However, due to the intrinsic asymmetry of nanowires, SNSPDs are usually very sensitive to the polarization of the incident radiation, their responsivity being maximum for light polarized parallel to the nanowire length (transverse-electric (TE) polarization). Here, we report on the reduction of the polarization sensitivity obtained by capping NbN-based SNSPDs with a high-index SiNx dielectric layer, which reduces the permittivity mismatch between the NbN wire and the surrounding area. Experimentally, a polarization sensitivity below 0.1 is obtained both at 1.31 and 1.55 mu m, in excellent agreement with simulations.

Place, publisher, year, edition, pages
OPTICAL SOC AMER, 2018
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-232251 (URN)10.1364/OE.26.017697 (DOI)000436226800140 ()2-s2.0-85048975081 (Scopus ID)
Funder
EU, Horizon 2020, 657497
Note

QC 20180720

Available from: 2018-07-20 Created: 2018-07-20 Last updated: 2019-05-21Bibliographically approved
7. Fractal superconducting nanowire single-photon detectors with reduced polarization sensitivity
Open this publication in new window or tab >>Fractal superconducting nanowire single-photon detectors with reduced polarization sensitivity
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2018 (English)In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 43, no 20, p. 5017-5020Article in journal (Refereed) Published
Abstract [en]

We demonstrate superconducting nanowire single-photon detectors (SNSPDs) based on a fractal design of the nanowires to reduce the polarization sensitivity of detection efficiency. We patterned niobium titanium nitride thin films into Peano curves with a linewidth of 100 nm and integrated the nanowires with optical microcavities to enhance their optical absorption. At a base temperature of 2.6 K, the fractal SNSPD exhibited a polarization-maximum device efficiency of 67% and a polarization-minimum device efficiency of 61% at a wavelength of 1550 nm. Therefore, the polarization sensitivity, defined as their ratio, was 1.1, lower than the polarization sensitivity of the SNSPDs in the meander design. The reduced polarization sensitivity of the detector could be maintained for higher-order spatial modes in multimode optical fibers and could tolerate misalignment between the optical mode and the detector. This fractal design is applicable to both amorphous and polycrystalline materials that are commonly used for making SNSPDs.

Place, publisher, year, edition, pages
OPTICAL SOC AMER, 2018
National Category
Other Engineering and Technologies
Identifiers
urn:nbn:se:kth:diva-238121 (URN)10.1364/OL.43.005017 (DOI)000447265700042 ()30320808 (PubMedID)2-s2.0-85054897619 (Scopus ID)
Note

QC 20181120

Available from: 2018-11-20 Created: 2018-11-20 Last updated: 2019-09-24Bibliographically approved
8. Entanglement distribution over a 96-km-long submarine optical fiber
Open this publication in new window or tab >>Entanglement distribution over a 96-km-long submarine optical fiber
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2019 (English)In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 116, no 14, p. 6684-6688Article in journal (Refereed) Published
Abstract [en]

Quantum entanglement is one of the most extraordinary effects in quantum physics, with many applications in the emerging field of quantum information science. In particular, it provides the foundation for quantum key distribution (QKD), which promises a conceptual leap in information security. Entanglement-based QKD holds great promise for future applications owing to the possibility of device-independent security and the potential of establishing global-scale quantum repeater networks. While other approaches to QKD have already reached the level of maturity required for operation in absence of typical laboratory infrastructure, comparable field demonstrations of entanglement-based QKD have not been performed so far. Here, we report on the successful distribution of polarization-entangled photon pairs between Malta and Sicily over 96 km of submarine optical telecommunications fiber. We observe around 257 photon pairs per second, with a polarization visibility above 90%. Our results show that QKD based on polarization entanglement is now indeed viable in long-distance fiber links. This field demonstration marks the longest-distance distribution of entanglement in a deployed telecommunications network and demonstrates an international submarine quantum communication channel. This opens up myriad possibilities for future experiments and technological applications using existing infrastructure.

Place, publisher, year, edition, pages
NATL ACAD SCIENCES, 2019
Keywords
quantum entanglement, quantum key distribution, quantum cryptography, polarization-entangled photons
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-249792 (URN)10.1073/pnas.1818752116 (DOI)000463069900034 ()30872476 (PubMedID)2-s2.0-85064055529 (Scopus ID)
Conference
AUSER JF, 1969, PHYSICAL REVIEW LETTERS, V23, P880
Note

QC 20190424

Available from: 2019-04-24 Created: 2019-04-24 Last updated: 2019-05-28Bibliographically approved

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