Integrated waveguides and deterministically positioned nitrogen vacancy centers in diamond created by femtosecond laser writing
John Patrick Hadden, Vibhav Bharadwaj, Belén Sotillo, Stefano Rampini, Roberto Osellame, Jeremy D. Witmer, Harishankar Jayakumar, Toney Teddy Fernandez, Andrea Chiappini, Cristina Armellini, Maurizio Ferrari, Roberta Ramponi, Paul E. Barclay, Shane Michael Eaton
Diamond's nitrogen vacancy (NV) center is an optically active defect with long spin coherence times, showing great potential for both efficient nanoscale magnetometry and quantum information processing schemes. Recently, both the formation of buried 3D optical waveguides and high-quality single NVs in diamond were demonstrated using the versatile femtosecond laser-writing technique. However, until now, combining these technologies has been an outstanding challenge. In this Letter, we fabricate laser-written photonic waveguides in quantum grade diamond which are aligned to within micron resolution to single laser-written NVs, enabling an integrated platform providing deterministically positioned waveguide-coupled NVs. This fabrication technology opens the way toward on-chip optical routing of single photons between NVs and optically integrated spin-based sensing.
Diamond's nitrogen vacancy (NV) center is an optically active defect with long spin coherence times, showing great potential for both efficient nanoscale magnetometry and quantum information processing schemes. Recently, both the formation of buried 3D optical waveguides and high-quality single NVs in diamond were demonstrated using the versatile femtosecond laser-writing technique. However, until now, combining these technologies has been an outstanding challenge. In this Letter, we fabricate laser-written photonic waveguides in quantum grade diamond which are aligned to within micron resolution to single laser-written NVs, enabling an integrated platform providing deterministically positioned waveguide-coupled NVs. This fabrication technology opens the way toward on-chip optical routing of single photons between NVs and optically integrated spin-based sensing.
Diamond's nitrogen vacancy (NV) center is an optically active defect with long spin coherence times, showing potential for efficient nanoscale magnetometry and entanglement schemes. Recently, both the formation of buried 3D optical waveguides and high quality single NVs in diamond were demonstrated using femtosecond laser-writing. However, until now, combining these technologies has been an outstanding challenge. In this work, we fabricate laser-written photonic circuits in diamond aligned within micron resolution to single laser-written NVs, enabling an integrated platform providing deterministically positioned waveguide-coupled NVs. This fabrication technology opens the way towards on-chip optical routing of single photons between NVs and optically integrated spin-based magnetometry.
Diamond’s nitrogen-vacancy (NV) center has been shown as a promising candidate for sensing applications and quantum computing because of its long electron spin coherence time and its ability to be found, manipulated and read out optically. An integrated photonics platform in diamond would be useful for NV-based magnetometry and quantum computing, in which NV centers are optically linked for long-range quantum entanglement due to the integration and stability provided by monolithic optical waveguides. Surface microchannels in diamond would be a great benefit for sensing applications, where NV centers could be used to probe biomolecules. In this work, we applied femtosecond laser writing to form buried 3D optical waveguides in diamond. By engineering the geometry of the type II waveguide, we obtained single mode guiding from visible to the infrared wavelengths. Further, we demonstrate the first Bragg waveguide in bulk diamond with narrowband reflection. We show the formation of single, high quality NV centers on demand in ultrapure diamond using a single pulse from a femtosecond laser. With these building blocks in place, we fabricated an integrated quantum photonic circuit containing optical waveguides coupled to NV centers deterministically placed within the waveguide. The single NVs were excited and their emission collected by the optical waveguides, allowing easy interfacing to standard optical fibers. We also report high aspect ratio surface microchannels, which we will integrate with laser-written NVs and waveguides, paving the way for ultrasensitive, nanoscale resolution biosensors.
Diamond is a promising platform for sensing and quantum processing owing to the remarkable properties of the nitrogen-vacancy (NV) impurity. The electrons of the NV center, largely localized at the vacancy site, combine to form a spin triplet, which can be polarized with 532 nm laser light, even at room temperature. The NV's states are isolated from environmental perturbations making their spin coherence comparable to trapped ions. An important breakthrough would be in connecting, using waveguides, multiple diamond NVs together optically. However, still lacking is an efficient photonic fabrication method for diamond akin to the photolithographic methods that have revolutionized silicon photonics. Here, we report the first demonstration of three dimensional buried optical waveguides in diamond, inscribed by focused femtosecond high repetition rate laser pulses. Within the waveguides, high quality NV properties are observed, making them promising for integrated magnetometer or quantum information systems on a diamond chip.
Quantum emitters, such as the negatively charged nitrogen-vacancy center in diamond, are attractive for quantum technologies, such as nano-sensing, quantum information processing, and as a non-classical light source. However, it is still challenging to position individual emitters in photonic structures while preserving the spin coherence properties of the defect. In this paper, we investigate single and ensemble waveguide-integrated nitrogen-vacancy centers in diamond fabricated by femtosecond laser writing followed by thermal annealing. Their spin coherence properties are systematically investigated and are shown to be comparable to native nitrogen-vacancy centers in diamond. This method paves the way for the fabrication of coherent spins integrated within photonic devices.
Integrated photonic circuits promise to be foundational for applications in quantum information and sensing technologies, through their ability to confine and manipulate light. A key role in such technologies may be played by spin-active quantum emitters, which can be used to store quantum information or as sensitive probes of the local environment. A leading candidate is the negatively charged nitrogen vacancy (NV−) diamond color center, whose ground spin state can be optically read out, exhibiting long (≈1 ms) coherence times at room temperature. These properties have driven research toward the integration of photonic circuits in the bulk of diamond with the development of techniques allowing fabrication of optical waveguides. In particular, femtosecond laser writing has emerged as a powerful technique, capable of writing light guiding structures with 3D configurations as well as creating NV complexes. In this Perspective, the physical mechanisms behind laser fabrication in diamond will be reviewed. The properties of waveguides, single- and ensemble-NV centers, will be analyzed, together with the possibility to combine such structures in integrated photonic devices, which can find direct application in quantum information and sensing.
Diamond is an exceptional material due to its hardness, high thermal conductivity and transparency from the UV to far IR. Recently it has caught the attention of the scientific community because it is the host of different color centers that can be used for magnetic sensing applications and quantum computing [1]. One of the most promising of these defects is the nitrogen-vacancy (NV) center. The electrons of the NV center, largely localized at the vacancy site, combine to form a spin triplet, which can be polarized with 532-nm laser light. The NV's states are isolated from environmental perturbations, making their spin coherence times long even at room temperature. The NVs can be easily initialized, manipulated and read out using light. Therefore, an important breakthrough would be in connecting, using optical waveguides, multiple diamond NVs.