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Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 21, Iss. 19 — Sep. 23, 2013
  • pp: 22657–22670
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High quantum-efficiency photon-number-resolving detector for photonic on-chip information processing

Brice Calkins, Paolo L. Mennea, Adriana E. Lita, Benjamin J. Metcalf, W. Steven Kolthammer, Antia Lamas-Linares, Justin B. Spring, Peter C. Humphreys, Richard P. Mirin, James C. Gates, Peter G. R. Smith, Ian A. Walmsley, Thomas Gerrits, and Sae Woo Nam  »View Author Affiliations


Optics Express, Vol. 21, Issue 19, pp. 22657-22670 (2013)
http://dx.doi.org/10.1364/OE.21.022657


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Abstract

The integrated optical circuit is a promising architecture for the realization of complex quantum optical states and information networks. One element that is required for many of these applications is a high-efficiency photon detector capable of photon-number discrimination. We present an integrated photonic system in the telecom band at 1550 nm based on UV-written silica-on-silicon waveguides and modified transition-edge sensors capable of number resolution and over 40 % efficiency. Exploiting the mode transmission failure of these devices, we multiplex three detectors in series to demonstrate a combined 79 % ± 2 % detection efficiency with a single pass, and 88 % ± 3 % at the operating wavelength of an on-chip terminal reflection grating. Furthermore, our optical measurements clearly demonstrate no significant unexplained loss in this system due to scattering or reflections. This waveguide and detector design therefore allows the placement of number-resolving single-photon detectors of predictable efficiency at arbitrary locations within a photonic circuit – a capability that offers great potential for many quantum optical applications. *Contribution of NIST, an agency of the U.S. government, not subject to copyright

© 2013 OSA

1. Introduction

Integrated optics has emerged as a leading technology to construct and manipulate complex quantum states of light, as desired for diverse applications in quantum information and communication. In contrast to bulk devices, photonic integrated circuits allow large-scale interferometric networks with excellent mode-matching, inherent phase-stability, and small footprints. Whilst quantum integrated photonic experiments have already shown on-chip two-photon quantum interference [2

2. A. Politi, M. J. Cryan, J. G. Rarity, S. Yu, and J. L. O’Brien, “Silica-on-silicon waveguide quantum circuits,” Science 320, 646–649 (2008). [CrossRef] [PubMed]

, 3

3. B. Smith, D. Kundys, N. L. Thomas-Peter, P. Smith, and I. Walmsley, “Phase-controlled integrated photonic quantum circuits,” Opt. Express 17, 13516–13525 (2009). [CrossRef] [PubMed]

], a current challenge is to further increase this complexity [4

4. B. J. Metcalf, N. Thomas-Peter, J. B. Spring, D. Kundys, M. A. Broome, P. Humphreys, X.-M. Jin, M. Barbieri, W. S. Kolthammer, J. C. Gates, B. J. Smith, N. K. Langford, P. G. R. Smith, and I. A. Walmsley, “Multiphoton quantum interference in a multiport integrated photonic device,” Nature Comm. 4, 1356 (2013). [CrossRef]

, 5

5. J. B. Spring, B. J. Metcalf, P. C. Humphreys, W. S. Kolthammer, X.-M. Jin, M. Barbieri, A. Datta, N. Thomas-Peter, N. K. Langford, D. Kundys, J. C. Gates, B. J. Smith, P. G. R. Smith, and I. A. Walmsley, “Boson sampling on a photonic chip,” Science 339, 798–801 (2013). [CrossRef]

]. This increase will require improved total device efficiencies spanning the generation, manipulation, and detection of single photons. A promising route is to engineer monolithic devices in which each of these functions occur on a single substrate, thus avoiding interface losses. To this end, a variety of approaches to on-chip photon sources [6

6. A. B. U’Ren, C. Silberhorn, K. Banaszek, and I. A. Walmsley, “Efficient conditional preparation of high-fidelity single photon states for fiber-optic quantum networks,” Phys. Rev. Lett. 93, 093601 (2004). [CrossRef]

, 7

7. A. Eckstein, A. Christ, P. J. Mosley, and C. Silberhorn, “Highly efficient single-pass source of pulsed single-mode twin beams of light,” Phys. Rev. Lett. 106, 13603 (2011). [CrossRef]

] and reconfigurable circuits [3

3. B. Smith, D. Kundys, N. L. Thomas-Peter, P. Smith, and I. Walmsley, “Phase-controlled integrated photonic quantum circuits,” Opt. Express 17, 13516–13525 (2009). [CrossRef] [PubMed]

, 8

8. P. J. Shadbolt, M. R. Verde, A. Peruzzo, A. Politi, A. Laing, M. Lobino, J. C. F. Matthews, M. G. Thompson, and J. L. O’Brien, “Generating, manipulating and measuring entanglement and mixture with a reconfigurable photonic circuit,” Nat. Photon. 6, 45–49 (2011). [CrossRef]

] are being pursued.

The first on-chip single-photon detectors have been recently realized by fabricating detectors that absorb the evanescent field of a guided wave. Adapting leading cryogenic superconducting detectors that had previously been used only as normal-incidence absorbers, evanescently-coupled on-chip detection has been achieved with a niobium nitride superconducting nanowire single-photon detector (SNSPD) [9

9. J. P. Sprengers, A. Gaggero, D. Sahin, S. Jahanmirinejad, G. Frucci, F. Mattioli, R. Leoni, J. Beetz, M. Lermer, M. Kamp, S. Höfling, R. Sanjines, and A. Fiore, “Waveguide superconducting single-photon detectors for integrated quantum photonic circuits,” Appl. Phys. Lett. 99, 181110 (2011). [CrossRef]

,10

10. W. H. P. Pernice, C. Schuck, O. Minaeva, M. Li, G. N. Goltsman, A. V. Sergienko, and H. X. Tang, “High-speed and high-efficiency travelling wave single-photon detectors embedded in nanophotonic circuits,” Nature Comm. 3, 1325 (2012). [CrossRef]

] and a tungsten transition edge sensor (TES) [11

11. T. Gerrits, N. Thomas-Peter, J. C. Gates, A. E. Lita, B. J. Metcalf, B. Calkins, N. A. Tomlin, A. E. Fox, A. Lamas-Linares, J. B. Spring, N. K. Langford, R. P. Mirin, P. G. R. Smith, I. A. Walmsley, and S. W. Nam, “On-chip, photon-number-resolving, telecommunication-band detectors for scalable photonic information processing,” Phys. Rev. A 84, 060301 (2011). [CrossRef]

]. Where SNSPDs provide exceptionally low timing jitter and a short recovery time [12

12. R. H. Hadfield, “Single-photon detectors for optical quantum information applications,” Nat Photon 3, 696–705 (2009). [CrossRef]

], TESs allow photon-number resolution with negligible dark counts [13

13. A. E. Lita, A. J. Miller, and S. W. Nam, “Counting near-infrared single-photons with 95% efficiency,” Opt. Express 16, 3032 (2008). [CrossRef] [PubMed]

]. In addition to avoiding losses from coupling off chip, these evanescently-coupled photon detectors offer a number of benefits compared to normal-incidence devices, including efficient detection over a wide range of wavelengths, polarization-dependent detection, arbitrary placement of a detector within a planar circuit, and transmission of the undetected signal. This final point means that a detector of low efficiency η is equivalent to a beamsplitter-detector system with a splitting ratio of (1 − η)/η with a detector of 100 % efficiency on the η-coupling arm. This capability is of great significance to quantum optics applications involving heralding or photon subtraction [14

14. T. Gerrits, S. Glancy, T. S. Clement, B. Calkins, A. E. Lita, A. J. Miller, A. L. Migdall, S. W. Nam, R. P. Mirin, and E. Knill, “Generation of optical coherent-state superpositions by number-resolved photon subtraction from the squeezed vacuum,” Phys. Rev. A 82, 031802 (2010). [CrossRef]

18

18. H. Takahashi, K. Wakui, S. Suzuki, M. Taakeoka, K. Hayasaka, A. Furusawa, and M. Sasaki, “Generation of large-amplitude coherent-state superposition via ancilla-assisted photon-subtraction,” Phys. Rev. Lett. 101, 233605/1–4 (2008). [CrossRef]

].

In order to realise the full potential of these on-chip detectors for use in more complex quantum photonic circuits they must replicate the high quantum efficiencies achieved by their bulk counterparts. In this paper we report an advance in the achievable quantum efficiency of an on-chip TES detector. By carefully designing the device geometry accounting for both the optical and thermal properties of the device we have achieved 43 % quantum efficiency. Taking advantage of the intrinsic photon-number resolution provided by the TES together with the fact that any undetected signal is transmitted along the waveguide, we have demonstrated that it is possible to achieve close to unity quantum efficiency by multiplexing several detectors along the guide. Using three detectors placed one after another, a total quantum efficiency of 79 % ± 2 % is realized. The addition of an integrated Bragg reflector after the final device increases this total detection efficiency to 88 % ± 3 %. These results are also in agreement with both theoretical optical modeling and room-temperature characterization of the device, which confirms the absence of significant scattering losses in the system and allows the performance of future detectors to be accurately assessed and optimized before use.

2. Device design

The concept behind the on-chip photon detectors used in this work is shown in Figure 1. A series of three TES photon-counting detectors is integrated with a UV-written single-mode waveguide. In order for this detector system to operate with high efficiency, number-resolution, and low scattering and reflective losses, both the optical characteristics of the waveguide/detector system and the electro-thermal characteristics of the TES device must be engineered appropriately. The basic designs of both systems are described in the following sections.

Fig. 1 On-chip photon detection scheme. (a) Three TES detectors with extended absorbers are operated in series on a single waveguide, resulting in a combined 79 % single-pass detection efficiency after correcting for fiber-coupling losses. Integrated Bragg gratings and two-way fiber coupling allows for the precise determination of each device efficiency without additional assumptions. (b) The extended-absorber detector utilizes a gold spine to increase thermal conduction and allow absorbed energy (from photons) to be detected by the TES (square device, center). (c) Simulated mode profile as light propagating in the waveguide is absorbed by the detector due to evanescent coupling.

2.1. Optical design

In order to obtain in-situ waveguide loss and detector absorption measurements for this device, a set of seven weak Bragg gratings were co-patterned with the waveguide via the process of Direct Grating Writing (DGW) [20

20. G. Emmerson, S. Watts, C. Gawith, V. Albanis, M. Ibsen, R. Williams, and P. Smith, “Fabrication of directly uv-written channel waveguides with simultaneously defined integral bragg gratings,” Electron. Lett. 38, 1531–1532 (2002). [CrossRef]

]. In DGW, a pair of focused continuous wave (CW) UV laser beams are overlapped to give an interference pattern. This pattern can then be modulated as it is translated along the sample to imprint either a continuous waveguide or a Bragg grating. The modulation pitch determines the Bragg wavelength and, due to the small spot size of the writing beam, wide spectral detuning is possible. The Bragg gratings were spectrally separated between 1500 nm and 1620 nm and were 1.5 mm in length. A Gaussian apodization profile was used to suppress grating sidebands. Additionally, a single high-reflectivity in-band grating 4 mm in length was added at the output end of the waveguide to permit a double-pass measurement to be made. This grating had a room-temperature center wavelength of 1553.3 nm with a 3 dB bandwidth of 0.6 nm. This center wavelength shifted to 1552.0 nm when cooled to the operating temperature of the TES due to thermal contraction.

Both ends of the waveguide were pigtailed with commercial fiber V-grooves, attached using an index-matched adhesive. The device was then mounted on a silicon base plate, which provided support and thermal anchoring of the fiber pigtails.

2.2. Detector design

In this work we describe a new approach to coupling light from an on-chip waveguide into a TES detector, making use of a separate-absorber geometry that increases the interaction length with the waveguide while maintaining a low enough total heat capacity to retain the photon-number resolving capability, which distinguishes the TES from all other types of single-photon detectors. Choosing to increase the interaction length while maintaining roughly the same extinction coefficient due to absorption in the device helps to reduce mode-mismatch at the interface between the bare waveguide and the device, which would cause unwanted reflections. The basic concept of this new device is shown in Fig. 1 (b). The active TES device is a 10 μm × 10 μm square of tungsten 40 nm thick that operates at its transition temperature of ≈ 84 millikelvin (mK). Attached to the device are two 100 μm long absorbers consisting of a bottom tungsten layer 3.5 μm wide and 40 nm thick, along with a gold layer 2 μm × 80 nm. The tungsten and gold layers are deposited by DC sputtering directly on top of the written waveguide structure and patterned by optical lithography and liftoff [11

11. T. Gerrits, N. Thomas-Peter, J. C. Gates, A. E. Lita, B. J. Metcalf, B. Calkins, N. A. Tomlin, A. E. Fox, A. Lamas-Linares, J. B. Spring, N. K. Langford, R. P. Mirin, P. G. R. Smith, I. A. Walmsley, and S. W. Nam, “On-chip, photon-number-resolving, telecommunication-band detectors for scalable photonic information processing,” Phys. Rev. A 84, 060301 (2011). [CrossRef]

, 22

22. B. Calkins, A. E. Lita, A. E. Fox, and S. W. Nam, “Faster recovery time of a hot-electron transition-edge sensor by use of normal metal heat-sinks,” Appl. Phys. Lett. 99, 241114 (2011). [CrossRef]

]. The majority of the evanescent photon absorption from the waveguide happens along the length of the two absorbers. The purpose of the gold spine is to increase heat conduction so that the energy of absorbed photons will be transmitted to the TES before escaping into the substrate. The details of the thermal model describing this device are contained in Section 3.2.

3. Modeling

3.1. Optical modeling

The evanescent field of the guided optical mode is absorbed by the tungsten/gold tails directly above the guiding layer. The simulations predict an absorption coefficient of 32.6 cm−1 (2.9 cm−1) for the TM-like (TE-like) guided modes. For the whole double-fin device (total length 210 μm) including the 10 μm TES square, an eigenmode-expansion method is used to propagate the modes under the detector to arrive at a predicted device efficiency of 50.3 % (6.1 %) for a TM-like (TE-like) input mode. Multiplexing three detectors one after another is thus predicted to achieve a total detector efficiency of 87.7 % for a TM-like input mode.

3.2. Detector modeling

When a photon is absorbed along the tails of these detectors, that energy must be transmitted to the active TES at the center before escaping through some other thermal path. At these temperatures the mechanism responsible for this thermal conduction is electron diffusion, and therefore its strength is proportional to both the ease with which electrons traverse through the material (electrical conductivity) and the average energy carried by each electron (kBT, where kB is the Boltzmann constant). The heat flow WF along the length of a metal with electrical conductivity σ and cross-sectional area A is described by the Wiedemann-Franz law [23

23. G. Wiedemann and R. Franz, “Ueber die waerme-leitungsfaehigkeit der metalle,” Annalen der Physik 165, 497–531 (1853). [CrossRef]

]:
Q˙WF(x)=σALTe(x)Te(x)x,
(1)
where Te is the electron temperature at position x in the wire and L is the Lorenz constant ( L=π2kB23e2=24.4 nW Ω K−2, where e is the electron charge). This conduction along the length of the spine is in competition with the thermal escape mechanism of electron-phonon coupling:
dQ˙ep(x)=ΣA(Te(x)5Tp5)dx,
(2)
where Σ is a material parameter quantifying the strength of the electron-phonon interaction and Te (Tp) are the electron (phonon) temperatures. The fact that the lateral heat conduction strength is linear with electron temperature and the heat escape strength carries an exponent of 5 is very important to the design of these devices. In the end, it means that a lower device operating temperature (Tc) is advantageous for thermalization of the device. In this study, the fabrication of devices did not focus on optimizing Tc for this purpose, and the relatively high Tc of ≈ 84 mK limited the maximum length of the detectors.

The temperature evolution of the detector tails can be determined by a one-dimensional heat equation:
γAdxT(x,t)dT(x,t)dt=Q˙WF(x,t)xdxdQ˙ep(x,t),
(3)
where γ is a material parameter characterizing the low-temperature electron specific heat of the metal (heat capacity C = γVT). Finally, the temperature evolution of the TES itself can be determined by use of standard models of TES electrothermal modeling [1

1. K. Irwin and G. Hilton, Cryogenic Particle Detection (Springer-Verlag, 2005), chap. Transition-Edge Sensors, pp. 63–150.

].

Table 1 lists pertinent material parameters for tungsten and gold. Note that the values for electrical conductivity assume bulk material, which will be valid so long as all device dimensions are much longer than the bulk electron mean free path lbulk. The final row shows the expected thermal conductivity κexp of a thin film 80 nm thick at temperature T = 100 mK. The κexp value for gold is based on the assumption that the mean free path will be limited by and equal to the thickness of the film. This is calculated as κexp=ne2lLTmvF where n is the free-electron density, m is the electron mass, and vF is the mean Fermi velocity.

Table 1. Thermal and electrical material parameters

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The advantage of using gold as a conductive spine material is seen in its nearly 20× higher thermal conductivity for this set of conditions. In addition, its lower specific heat allows the addition of more material while maintaining similar total heat capacity. However, the higher electron-phonon coupling strength in gold enhances the energy escape mechanism. The right balance must be found in order to ensure a functional device.

In order to understand how the choice of device geometry will affect the photon-number resolution performance of the device, we used a finite-element simulation to predict the ideal current-pulse that will be measured at the TES due to photon absorption events at many locations along the length of the absorbers. These predictions, combined with the expected noise spectrum of our TES [31

31. We assume a typical simple model for the noise spectrum of the device as per Ref [1]. We find experimentally that this model fits reasonably well, although a more sophisticated approach will be necessary to describe the noise of these devices exactly.

], allows us to estimate the energy resolution of a device with a particular set of design parameters. A sample of the thermal modeling is shown in Fig. 2 for the particular design that is the subject of this work.

Fig. 2 Operation of extended-absorber device. (a) Simulation of electron-system temperature evolution vs position on device after a 1550 nm photon is absorbed at x = +80 μm on one of the tails at t = 0. Black lines indicate borders of 10 μm square at center of device and show the temperature evolution of the TES itself. (b) Resulting simulated change in current flowing through the device, now shown for multiple impact points between xi = 0μm (red) and xi = +100μm (blue) in 10 μm steps.

Fig. 3 Simulated and measured detector performance. (a) Thermal modeling. The red line shows the predicted energy resolution of the device as a function of detector length. Dotted lines indicate the standard error on the model. The circles represent the measured energy resolution of the three fabricated detectors. The spread of measured energy resolution values is likely due to differences in the superconducting-to-normal transition properties between the three detectors. (b) Optical modeling. The black lines show the predicted optical absorption efficiency of the TM and TE modes as a function of whole detector length. The inset shows the measured photon-detection efficiency of the TM mode for the three detectors.

4. Device measurements

In order to determine the efficiency of each photon detector with the minimum number of assumptions, several steps were taken. First, the coupling of fiber at both ends of the waveguide under test allows a direct measurement of not only the efficiency of each detector but also the coupling loss at each end of the waveguide. The details of this procedure are given in Section 4.1. Second, the inclusion of diagnostic Bragg gratings at several locations along the waveguide allows a direct measurement of not only the waveguide propagation loss but also provides an additional measurement of the fraction of light that is absorbed by each detector. These measurements are described in Section 4.2.

4.1. Quantum efficiency measurements

Measurement of the total device and individual TES detection efficiency was done following a similar scheme as described earlier [11

11. T. Gerrits, N. Thomas-Peter, J. C. Gates, A. E. Lita, B. J. Metcalf, B. Calkins, N. A. Tomlin, A. E. Fox, A. Lamas-Linares, J. B. Spring, N. K. Langford, R. P. Mirin, P. G. R. Smith, I. A. Walmsley, and S. W. Nam, “On-chip, photon-number-resolving, telecommunication-band detectors for scalable photonic information processing,” Phys. Rev. A 84, 060301 (2011). [CrossRef]

]. In the present study, we measured the photon response for three in-line detectors simultaneously. Figure 4 shows a schematic of the experimental setup. A 1550 nm pulsed diode laser produced nanosecond pulses at a repetition rate of 100 kHz, typically at a few μW average power. The optical fiber switch and calibrated power meter allowed both a measurement of the un-attenuated laser power and a calibration of each of the three in-line variable fiber attenuators [32

32. A. J. Miller, A. E. Lita, B. Calkins, I. Vayshenker, S. M. Gruber, and S. W. Nam, “Compact cryogenic self-aligning fiber-to-detector coupling with losses below one percent,” Opt. Express 19, 9102–9110 (2011). [CrossRef] [PubMed]

]. Subsequent to these measurements the laser pulses were attenuated to the single-photon regime by use of all three calibrated attenuators, and this photon flux is switched towards the device. By this, we can determine the input mean photon number per laser pulse, in. The fiber polarization controller allowed tuning the polarization entering the waveguide chip. We used polarization-maintaining fiber after the optical fiber switch all the way to the waveguide chip, which was mounted inside a copper shield attached to the cold-stage of a commercial adiabatic demagnetization refrigerator (ADR) at a temperature of ∼ 50 mK. The detector region consisted of an array of three TESs with 100 μm long absorbers on each side. A high-reflectivity grating was placed on one end of the detector array to allow double-pass detection at the grating peak wavelength of 1552.0 ± 0.1 nm. When measuring the photon response of the detector array for each direction (A → B and B → A), an accurate determination of all individual TES detection efficiencies as well as the fiber-waveguide coupling efficiencies was possible.

Fig. 4 Schematic of the experimental setup. Each TES requires its own SQUID and readout electronics. Bottom: detailed view of the on-chip TES showing the different launch directions A and B, the three detector efficiencies, η1, η2, η3 and the fiber-coupling efficiencies, ηA and ηB. The weak reflectivity integrated Bragg gratings are used to make a room-temperature characterization of device performance whilst the high-reflectivity grating at the end of the device provides a double-pass of the detectors for an appropriately tuned source launched into port A.

Light pulses with known mean photon number in can be coupled to the structure and detector array from the two facets of the device (A and B). The reflection gratings are weak reflectors at different wavelengths, ranging from 1500 nm to 1620 nm. These gratings are used to measure the in-situ loss of the waveguide structure, revealing the portion of loss associated with the placement of a detector on top of the waveguide structure as well as the propagation loss in the waveguide itself, as described in Section 5.2. When measuring the individual detector response for both possible propagation directions (A → B and B → A), a total of six measurements are done. The outcomes of all six measurements are captured by six equations:
N¯1=ηAeαL1η1N¯inN¯1'=ηBeα(L1+2L2)(1η3)(1η2)η1N¯inN¯2=ηAeα(L1+L2)(1η1)η2N¯inN¯2'=ηBeα(L1+L2)(1η3)η2N¯inN¯3=ηAeα(L1+2L2)(1η1)(1η2)η3N¯inN¯3'=ηBeαL1η3N¯in,
(4)
where 1/2/3 (N̄′1/2/3) are the measured mean photon numbers at TES 1, TES 2 and TES 3, respectively for propagation direction A → B (B → A). in is the derived input mean photon number inside the polarization-maintaining fiber leading towards the waveguide structure. ηA/B are the fiber-waveguide coupling efficiencies. α is the measured waveguide-propagation extinction coefficient (Section 5.2), and L1 (L2) is the length of the waveguide between the edge of the chip and the first detector (between the first and second detector). As only five unknowns exist, the parameters are overdetermined and a simple least-mean-squares fitting routine using Eq. 4 yields the individual detection efficiencies. To generalize this technique, the use of N detectors in series results in 2N measurements and N + 2 unknowns, and therefore N = 3 is the minimum number of detectors needed in order to overdetermine the resulting set of parameters. The above relations allow us to accurately extract values for both the detection efficiencies for photons that have been coupled into the waveguide and, independently, the coupling efficiencies at each facet of the device.

4.2. Optical loss measurements

In addition to the quantum efficiency measurements conducted using the TES detectors, room-temperature characterization was conducted using the integrated Bragg gratings with high-intensity light. The grating-based loss measurement technique detailed in [33

33. H. L. Rogers, S. Ambran, C. Holmes, P. G. R. Smith, and J. C. Gates, “In situ loss measurement of direct uv-written waveguides using integrated bragg gratings,” Opt. Lett. 35, 2849–2851 (2010). [CrossRef] [PubMed]

] was used to provide a relative power profile along the length of the waveguide. This ratiometric approach allows the loss profile to be determined independent of any coupling losses, and since gratings are positioned between each TES element, the loss associated with each of the three detector regions may be determined.

Characterization was carried out both before and after the deposition of the TES layer. The former of these measurements allowed the waveguide loss to be extracted, while the latter provided absorption values for each of the detectors. In each case, a reflection spectrum was collected while launching broadband light into each end of the waveguide. Least-mean-squares fitting of the resulting Bragg reflection peaks was then conducted to obtain values for the peak power reflected by each grating. Section 5.2 details the results of these measurements.

5. Results

Table 2 presents the individual detection efficiencies η1/2/3 and coupling efficiencies ηA/B based on all measurements for both polarization states. Table 3 presents the measured detector absorption ηabs,1/2/3 arising from the grating reflection measurements. The agreement between most of these values (i.e., η1/2/3 = ηabs,1/2/3) is a demonstration of both the inherent 100 % internal detection efficiency of the optical TES (a property that has been reported elsewhere [11

11. T. Gerrits, N. Thomas-Peter, J. C. Gates, A. E. Lita, B. J. Metcalf, B. Calkins, N. A. Tomlin, A. E. Fox, A. Lamas-Linares, J. B. Spring, N. K. Langford, R. P. Mirin, P. G. R. Smith, I. A. Walmsley, and S. W. Nam, “On-chip, photon-number-resolving, telecommunication-band detectors for scalable photonic information processing,” Phys. Rev. A 84, 060301 (2011). [CrossRef]

, 32

32. A. J. Miller, A. E. Lita, B. Calkins, I. Vayshenker, S. M. Gruber, and S. W. Nam, “Compact cryogenic self-aligning fiber-to-detector coupling with losses below one percent,” Opt. Express 19, 9102–9110 (2011). [CrossRef] [PubMed]

]), as well as the lack of significant inherent scattering mechanisms between the detectors. The few-percent mismatch for some of the values may be the result of differing surface contaminations causing additional losses in the two separate measurements.

Table 2. Derived individual detector efficiencies η1/2/3 and fiber-waveguide coupling efficiencies ηA/B. Derivations based on Eqn. 4

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Table 3. Classically obtained losses at each detector element ηabs,1/2/3, based on a grating based loss measurement.

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5.1. Quantum efficiency results

Fig. 5 Response curve density plot for all three TES, while sending triggered photon pulses from A to B. Pulse-collections of increasing height correspond to increasing numbers of photons detected per pulse. The mean number of photons per pulse decreases as the light travels from detector 1 to detector 3 (bottom to top) due to absorption of the preceeding TES.

The derived detection efficiencies for the TM input polarization are 43.7 %±0.7 %, 43.6 %± 0.5 % and 43.2 % ± 0.7 % for TES 1, TES 2 and TES 3, respectively. The combined efficiency of all three detectors is 79 % ± 2 % [34

34. The uncertainties quoted for the individual detector efficiencies include only the standard deviation of experimentally measured values, whereas the combined results also include the 1−σ uncertainty due to the calibration of the optical setup.

]. Additionally, by employing a tunable CW laser source we could utilize the high-reflectivity grating at the end of the device, resulting in a measured increase of this combined detector efficiency to 88 % ± 3 %. Since light could only be launched into port ‘A’ for this measurement, we calculated η1/2/3 simply using the measured photon counts assuming that ηA and α remained unchanged. This result is consistent with the measured ∼ 50 % reflectivity of the terminal grating.

5.2. Optical loss results

Figure 6 displays the relative power profile of the device for the TM polarization. The difference in relative power on either side of each of the tungsten regions, after subtracting the measured waveguide loss over this distance (0.920 ± 0.020 dB/cm and 0.947 ± 0.023 dB/cm for TE and TM respectively), gives an estimate of the power coupled into the detector. The average absorption at each TES was thus found to be 46.7% (43.2%±0.6%, 48.8%±0.6%, 48.2%±0.6%) for TM and 5.3% (6.3%±0.6%, 4.4%±0.7%, 5.3%±0.6%) for TE. These values include both the absorption within the tungsten and any scattering at the interfaces on either side of this region, though modeling suggests that this scattering is small. The values are in very good agreement with the detection efficiency measurements above, implying that radiative and reflective losses due to the detector are minimal, an important conclusion that could not be verified in an earlier study [11

11. T. Gerrits, N. Thomas-Peter, J. C. Gates, A. E. Lita, B. J. Metcalf, B. Calkins, N. A. Tomlin, A. E. Fox, A. Lamas-Linares, J. B. Spring, N. K. Langford, R. P. Mirin, P. G. R. Smith, I. A. Walmsley, and S. W. Nam, “On-chip, photon-number-resolving, telecommunication-band detectors for scalable photonic information processing,” Phys. Rev. A 84, 060301 (2011). [CrossRef]

].

Fig. 6 The relative power profile obtained for the TM-like mode of the device, each point corresponding to a grating. Red (blue) marks indicate measurements taken before (after) TES deposition. R’ and R” are the grating peak powers measured in reflection from the forward and reverse launches, respectively. Both waveguide propagation loss and detector absorption can be inferred from these measurements.

6. Conclusions

We have demonstrated a high-efficiency number-resolving photon detector integrated on-chip with a single-mode waveguide – a critical component for many applications in quantum information. In addition, we have shown the utility of chip-edge optical-fiber coupling and integrated Bragg gratings for device diagnostics, allowing us to determine device and coupling efficiencies to within a few percent without additional assumptions. The fact that the two independent measurements of detector absorption and detection efficiency are consistent demonstrates the absence of additional photon-loss mechanisms, meaning that these devices (even with low efficiency) are analogous to 100 % efficient heralding detectors. This initial test of the extended-absorber TES demonstrates the potential for high-efficiency waveguide-integrated photon-counting detectors. Additional improvements and optimization of this design hold the promise of achieving near-unity efficiency while retaining true photon-number resolution – one of the ultimate goals for detectors in any quantum optical system.

Acknowledgments

This work was supported by the NIST Quantum Information Initiative and by the EPSRC (Engineering and Physical Sciences Research Council) (grant no. GR/S82176/01), EU IP (Integrated Project) Q-ESSENCE (Quantum Interfaces, sensors, and communication based on entanglement). IAW acknowledges a Royal Society/Wolfson Research Merit Award.

References and links

1.

K. Irwin and G. Hilton, Cryogenic Particle Detection (Springer-Verlag, 2005), chap. Transition-Edge Sensors, pp. 63–150.

2.

A. Politi, M. J. Cryan, J. G. Rarity, S. Yu, and J. L. O’Brien, “Silica-on-silicon waveguide quantum circuits,” Science 320, 646–649 (2008). [CrossRef] [PubMed]

3.

B. Smith, D. Kundys, N. L. Thomas-Peter, P. Smith, and I. Walmsley, “Phase-controlled integrated photonic quantum circuits,” Opt. Express 17, 13516–13525 (2009). [CrossRef] [PubMed]

4.

B. J. Metcalf, N. Thomas-Peter, J. B. Spring, D. Kundys, M. A. Broome, P. Humphreys, X.-M. Jin, M. Barbieri, W. S. Kolthammer, J. C. Gates, B. J. Smith, N. K. Langford, P. G. R. Smith, and I. A. Walmsley, “Multiphoton quantum interference in a multiport integrated photonic device,” Nature Comm. 4, 1356 (2013). [CrossRef]

5.

J. B. Spring, B. J. Metcalf, P. C. Humphreys, W. S. Kolthammer, X.-M. Jin, M. Barbieri, A. Datta, N. Thomas-Peter, N. K. Langford, D. Kundys, J. C. Gates, B. J. Smith, P. G. R. Smith, and I. A. Walmsley, “Boson sampling on a photonic chip,” Science 339, 798–801 (2013). [CrossRef]

6.

A. B. U’Ren, C. Silberhorn, K. Banaszek, and I. A. Walmsley, “Efficient conditional preparation of high-fidelity single photon states for fiber-optic quantum networks,” Phys. Rev. Lett. 93, 093601 (2004). [CrossRef]

7.

A. Eckstein, A. Christ, P. J. Mosley, and C. Silberhorn, “Highly efficient single-pass source of pulsed single-mode twin beams of light,” Phys. Rev. Lett. 106, 13603 (2011). [CrossRef]

8.

P. J. Shadbolt, M. R. Verde, A. Peruzzo, A. Politi, A. Laing, M. Lobino, J. C. F. Matthews, M. G. Thompson, and J. L. O’Brien, “Generating, manipulating and measuring entanglement and mixture with a reconfigurable photonic circuit,” Nat. Photon. 6, 45–49 (2011). [CrossRef]

9.

J. P. Sprengers, A. Gaggero, D. Sahin, S. Jahanmirinejad, G. Frucci, F. Mattioli, R. Leoni, J. Beetz, M. Lermer, M. Kamp, S. Höfling, R. Sanjines, and A. Fiore, “Waveguide superconducting single-photon detectors for integrated quantum photonic circuits,” Appl. Phys. Lett. 99, 181110 (2011). [CrossRef]

10.

W. H. P. Pernice, C. Schuck, O. Minaeva, M. Li, G. N. Goltsman, A. V. Sergienko, and H. X. Tang, “High-speed and high-efficiency travelling wave single-photon detectors embedded in nanophotonic circuits,” Nature Comm. 3, 1325 (2012). [CrossRef]

11.

T. Gerrits, N. Thomas-Peter, J. C. Gates, A. E. Lita, B. J. Metcalf, B. Calkins, N. A. Tomlin, A. E. Fox, A. Lamas-Linares, J. B. Spring, N. K. Langford, R. P. Mirin, P. G. R. Smith, I. A. Walmsley, and S. W. Nam, “On-chip, photon-number-resolving, telecommunication-band detectors for scalable photonic information processing,” Phys. Rev. A 84, 060301 (2011). [CrossRef]

12.

R. H. Hadfield, “Single-photon detectors for optical quantum information applications,” Nat Photon 3, 696–705 (2009). [CrossRef]

13.

A. E. Lita, A. J. Miller, and S. W. Nam, “Counting near-infrared single-photons with 95% efficiency,” Opt. Express 16, 3032 (2008). [CrossRef] [PubMed]

14.

T. Gerrits, S. Glancy, T. S. Clement, B. Calkins, A. E. Lita, A. J. Miller, A. L. Migdall, S. W. Nam, R. P. Mirin, and E. Knill, “Generation of optical coherent-state superpositions by number-resolved photon subtraction from the squeezed vacuum,” Phys. Rev. A 82, 031802 (2010). [CrossRef]

15.

A. Ourjoumtsev, R. Tualle-Brouri, J. Laurat, and P. Grangier, “Generating optical schroedinger kittens for quantum information processing,” Science 312, 83–86 (2006). [CrossRef] [PubMed]

16.

J. S. Neergaard-Nielsen, B. M. Nielsen, C. Hettich, K. Molmer, and E. S. Polzik, “Generation of a superposition of odd photon number states for quantum information networks,” Phys. Rev. Lett. 97, 083604/1–4 (2006). [CrossRef]

17.

K. Wakui, H. Takahashi, A. Furusawa, and M. Sasaki, “Photon subtracted squeezed states generated with periodically poled KTiOPO4,” Opt. Express 15, 3568–3574 (2007). [CrossRef] [PubMed]

18.

H. Takahashi, K. Wakui, S. Suzuki, M. Taakeoka, K. Hayasaka, A. Furusawa, and M. Sasaki, “Generation of large-amplitude coherent-state superposition via ancilla-assisted photon-subtraction,” Phys. Rev. Lett. 101, 233605/1–4 (2008). [CrossRef]

19.

D. Zauner, K. Kulstad, J. Rathje, and M. Svalgaard, “Directly uv-written silica-on-silicon planar waveguides with low insertion loss,” Electron. Lett. 34, 1582–1584 (1998). [CrossRef]

20.

G. Emmerson, S. Watts, C. Gawith, V. Albanis, M. Ibsen, R. Williams, and P. Smith, “Fabrication of directly uv-written channel waveguides with simultaneously defined integral bragg gratings,” Electron. Lett. 38, 1531–1532 (2002). [CrossRef]

21.

A. J. Miller, S. W. Nam, J. M. Martinis, and A. V. Sergienko, “Demonstration of a low-noise near-infrared photon counter with multiphoton discrimination,” Appl. Phys. Lett. 83, 791–793 (2003). [CrossRef]

22.

B. Calkins, A. E. Lita, A. E. Fox, and S. W. Nam, “Faster recovery time of a hot-electron transition-edge sensor by use of normal metal heat-sinks,” Appl. Phys. Lett. 99, 241114 (2011). [CrossRef]

23.

G. Wiedemann and R. Franz, “Ueber die waerme-leitungsfaehigkeit der metalle,” Annalen der Physik 165, 497–531 (1853). [CrossRef]

24.

C. Kittel, Introduction to Solid State Physics (John Wiley & Sons, Inc., 2005), 8th ed.

25.

B. Cabrera, “Introduction to tes physics,” J. Low Temp. Phys. 151, 82 (2008). [CrossRef]

26.

P. M. Echternach, M. R. Thoman, C. M. Gould, and H. M. Bozler, “Electron-phonon scattering rates in disordered metallic films below 1 k,” Phys. Rev. B 46, 10339 (1980). [CrossRef]

27.

Value is based on experimentally measured low-temperature normal resistance of ≈ 10 Ω for a 20 nm thick square device. Note that this is for a W film that consists of a mixture of crystallographic phases and is not typical for bulk W.

28.

C. Y. Ho, R. W. Powell, and P. E. Liley, Thermal Conductivity of the Elements: A Comprehensive Review (American Chemical Society).

29.

P. J. Feenan, A. Myers, and D. Sang, “De haas-van alphen measurements of the electron cyclotron mass in w,” Solid State Commun. 16, 35–39 (1975). [CrossRef]

30.

N. A. D. Mermin, Solid State Physics (Saunders College Publishing, 1976).

31.

We assume a typical simple model for the noise spectrum of the device as per Ref [1]. We find experimentally that this model fits reasonably well, although a more sophisticated approach will be necessary to describe the noise of these devices exactly.

32.

A. J. Miller, A. E. Lita, B. Calkins, I. Vayshenker, S. M. Gruber, and S. W. Nam, “Compact cryogenic self-aligning fiber-to-detector coupling with losses below one percent,” Opt. Express 19, 9102–9110 (2011). [CrossRef] [PubMed]

33.

H. L. Rogers, S. Ambran, C. Holmes, P. G. R. Smith, and J. C. Gates, “In situ loss measurement of direct uv-written waveguides using integrated bragg gratings,” Opt. Lett. 35, 2849–2851 (2010). [CrossRef] [PubMed]

34.

The uncertainties quoted for the individual detector efficiencies include only the standard deviation of experimentally measured values, whereas the combined results also include the 1−σ uncertainty due to the calibration of the optical setup.

OCIS Codes
(030.5260) Coherence and statistical optics : Photon counting
(040.3780) Detectors : Low light level
(220.0220) Optical design and fabrication : Optical design and fabrication
(230.7390) Optical devices : Waveguides, planar
(270.5570) Quantum optics : Quantum detectors

ToC Category:
Detectors

History
Original Manuscript: May 24, 2013
Revised Manuscript: July 1, 2013
Manuscript Accepted: July 10, 2013
Published: September 18, 2013

Virtual Issues
September 19, 2013 Spotlight on Optics

Citation
Brice Calkins, Paolo L. Mennea, Adriana E. Lita, Benjamin J. Metcalf, W. Steven Kolthammer, Antia Lamas-Linares, Justin B. Spring, Peter C. Humphreys, Richard P. Mirin, James C. Gates, Peter G. R. Smith, Ian A. Walmsley, Thomas Gerrits, and Sae Woo Nam, "High quantum-efficiency photon-number-resolving detector for photonic on-chip information processing," Opt. Express 21, 22657-22670 (2013)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-19-22657


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References

  1. K. Irwin and G. Hilton, Cryogenic Particle Detection (Springer-Verlag, 2005), chap. Transition-Edge Sensors, pp. 63–150.
  2. A. Politi, M. J. Cryan, J. G. Rarity, S. Yu, and J. L. O’Brien, “Silica-on-silicon waveguide quantum circuits,” Science320, 646–649 (2008). [CrossRef] [PubMed]
  3. B. Smith, D. Kundys, N. L. Thomas-Peter, P. Smith, and I. Walmsley, “Phase-controlled integrated photonic quantum circuits,” Opt. Express17, 13516–13525 (2009). [CrossRef] [PubMed]
  4. B. J. Metcalf, N. Thomas-Peter, J. B. Spring, D. Kundys, M. A. Broome, P. Humphreys, X.-M. Jin, M. Barbieri, W. S. Kolthammer, J. C. Gates, B. J. Smith, N. K. Langford, P. G. R. Smith, and I. A. Walmsley, “Multiphoton quantum interference in a multiport integrated photonic device,” Nature Comm.4, 1356 (2013). [CrossRef]
  5. J. B. Spring, B. J. Metcalf, P. C. Humphreys, W. S. Kolthammer, X.-M. Jin, M. Barbieri, A. Datta, N. Thomas-Peter, N. K. Langford, D. Kundys, J. C. Gates, B. J. Smith, P. G. R. Smith, and I. A. Walmsley, “Boson sampling on a photonic chip,” Science339, 798–801 (2013). [CrossRef]
  6. A. B. U’Ren, C. Silberhorn, K. Banaszek, and I. A. Walmsley, “Efficient conditional preparation of high-fidelity single photon states for fiber-optic quantum networks,” Phys. Rev. Lett.93, 093601 (2004). [CrossRef]
  7. A. Eckstein, A. Christ, P. J. Mosley, and C. Silberhorn, “Highly efficient single-pass source of pulsed single-mode twin beams of light,” Phys. Rev. Lett.106, 13603 (2011). [CrossRef]
  8. P. J. Shadbolt, M. R. Verde, A. Peruzzo, A. Politi, A. Laing, M. Lobino, J. C. F. Matthews, M. G. Thompson, and J. L. O’Brien, “Generating, manipulating and measuring entanglement and mixture with a reconfigurable photonic circuit,” Nat. Photon.6, 45–49 (2011). [CrossRef]
  9. J. P. Sprengers, A. Gaggero, D. Sahin, S. Jahanmirinejad, G. Frucci, F. Mattioli, R. Leoni, J. Beetz, M. Lermer, M. Kamp, S. Höfling, R. Sanjines, and A. Fiore, “Waveguide superconducting single-photon detectors for integrated quantum photonic circuits,” Appl. Phys. Lett.99, 181110 (2011). [CrossRef]
  10. W. H. P. Pernice, C. Schuck, O. Minaeva, M. Li, G. N. Goltsman, A. V. Sergienko, and H. X. Tang, “High-speed and high-efficiency travelling wave single-photon detectors embedded in nanophotonic circuits,” Nature Comm.3, 1325 (2012). [CrossRef]
  11. T. Gerrits, N. Thomas-Peter, J. C. Gates, A. E. Lita, B. J. Metcalf, B. Calkins, N. A. Tomlin, A. E. Fox, A. Lamas-Linares, J. B. Spring, N. K. Langford, R. P. Mirin, P. G. R. Smith, I. A. Walmsley, and S. W. Nam, “On-chip, photon-number-resolving, telecommunication-band detectors for scalable photonic information processing,” Phys. Rev. A84, 060301 (2011). [CrossRef]
  12. R. H. Hadfield, “Single-photon detectors for optical quantum information applications,” Nat Photon3, 696–705 (2009). [CrossRef]
  13. A. E. Lita, A. J. Miller, and S. W. Nam, “Counting near-infrared single-photons with 95% efficiency,” Opt. Express16, 3032 (2008). [CrossRef] [PubMed]
  14. T. Gerrits, S. Glancy, T. S. Clement, B. Calkins, A. E. Lita, A. J. Miller, A. L. Migdall, S. W. Nam, R. P. Mirin, and E. Knill, “Generation of optical coherent-state superpositions by number-resolved photon subtraction from the squeezed vacuum,” Phys. Rev. A82, 031802 (2010). [CrossRef]
  15. A. Ourjoumtsev, R. Tualle-Brouri, J. Laurat, and P. Grangier, “Generating optical schroedinger kittens for quantum information processing,” Science312, 83–86 (2006). [CrossRef] [PubMed]
  16. J. S. Neergaard-Nielsen, B. M. Nielsen, C. Hettich, K. Molmer, and E. S. Polzik, “Generation of a superposition of odd photon number states for quantum information networks,” Phys. Rev. Lett.97, 083604/1–4 (2006). [CrossRef]
  17. K. Wakui, H. Takahashi, A. Furusawa, and M. Sasaki, “Photon subtracted squeezed states generated with periodically poled KTiOPO4,” Opt. Express15, 3568–3574 (2007). [CrossRef] [PubMed]
  18. H. Takahashi, K. Wakui, S. Suzuki, M. Taakeoka, K. Hayasaka, A. Furusawa, and M. Sasaki, “Generation of large-amplitude coherent-state superposition via ancilla-assisted photon-subtraction,” Phys. Rev. Lett.101, 233605/1–4 (2008). [CrossRef]
  19. D. Zauner, K. Kulstad, J. Rathje, and M. Svalgaard, “Directly uv-written silica-on-silicon planar waveguides with low insertion loss,” Electron. Lett.34, 1582–1584 (1998). [CrossRef]
  20. G. Emmerson, S. Watts, C. Gawith, V. Albanis, M. Ibsen, R. Williams, and P. Smith, “Fabrication of directly uv-written channel waveguides with simultaneously defined integral bragg gratings,” Electron. Lett.38, 1531–1532 (2002). [CrossRef]
  21. A. J. Miller, S. W. Nam, J. M. Martinis, and A. V. Sergienko, “Demonstration of a low-noise near-infrared photon counter with multiphoton discrimination,” Appl. Phys. Lett.83, 791–793 (2003). [CrossRef]
  22. B. Calkins, A. E. Lita, A. E. Fox, and S. W. Nam, “Faster recovery time of a hot-electron transition-edge sensor by use of normal metal heat-sinks,” Appl. Phys. Lett.99, 241114 (2011). [CrossRef]
  23. G. Wiedemann and R. Franz, “Ueber die waerme-leitungsfaehigkeit der metalle,” Annalen der Physik165, 497–531 (1853). [CrossRef]
  24. C. Kittel, Introduction to Solid State Physics (John Wiley & Sons, Inc., 2005), 8th ed.
  25. B. Cabrera, “Introduction to tes physics,” J. Low Temp. Phys.151, 82 (2008). [CrossRef]
  26. P. M. Echternach, M. R. Thoman, C. M. Gould, and H. M. Bozler, “Electron-phonon scattering rates in disordered metallic films below 1 k,” Phys. Rev. B46, 10339 (1980). [CrossRef]
  27. Value is based on experimentally measured low-temperature normal resistance of ≈ 10 Ω for a 20 nm thick square device. Note that this is for a W film that consists of a mixture of crystallographic phases and is not typical for bulk W.
  28. C. Y. Ho, R. W. Powell, and P. E. Liley, Thermal Conductivity of the Elements: A Comprehensive Review (American Chemical Society).
  29. P. J. Feenan, A. Myers, and D. Sang, “De haas-van alphen measurements of the electron cyclotron mass in w,” Solid State Commun.16, 35–39 (1975). [CrossRef]
  30. N. A. D. Mermin, Solid State Physics (Saunders College Publishing, 1976).
  31. We assume a typical simple model for the noise spectrum of the device as per Ref [1]. We find experimentally that this model fits reasonably well, although a more sophisticated approach will be necessary to describe the noise of these devices exactly.
  32. A. J. Miller, A. E. Lita, B. Calkins, I. Vayshenker, S. M. Gruber, and S. W. Nam, “Compact cryogenic self-aligning fiber-to-detector coupling with losses below one percent,” Opt. Express19, 9102–9110 (2011). [CrossRef] [PubMed]
  33. H. L. Rogers, S. Ambran, C. Holmes, P. G. R. Smith, and J. C. Gates, “In situ loss measurement of direct uv-written waveguides using integrated bragg gratings,” Opt. Lett.35, 2849–2851 (2010). [CrossRef] [PubMed]
  34. The uncertainties quoted for the individual detector efficiencies include only the standard deviation of experimentally measured values, whereas the combined results also include the 1−σ uncertainty due to the calibration of the optical setup.

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