Silica-on-Silicon Waveguide Quantum Circuits

Abstract

Quantum technologies based on photons are anticipated in the areas of information processing, communication, metrology, and lithography. While there have been impressive proof-of-principle demonstrations in all of these areas, future technologies will likely require an integrated optics architecture for improved performance, miniaturization and scalability. We demonstrated highfidelity silica-on-silicon integrated optical realizations of key quantum photonic circuits, including two-photon quantum interference with a visibility of 94.8±0.5%; a controlled-NOT gate with logical basis fidelity of 94.3 ± 0.2%; and a path entangled state of two photons with fidelity > 92%.Quantum information science [1] has shown that harnessing quantum mechanical effects can dramatically improve performance for certain tasks in communication, computation and measurement. However, realizing such quantum technologies is an immense challenge, owing to the difficulty in controlling quantum systems and their inherent fragility. Of the various physical systems being pursued, single particles of light-photons-are often the logical choice, and have been widely used in quantum communication [2], quantum metrology [3,4,5], and quantum lithography [6] settings. Low noise (or decoherence) also makes photons attractive quantum bits (or qubits), and they have emerged as a leading approach to quantum information processing [7].In addition to single photon sources [8] and detectors [9], photonic quantum technologies will rely on sophisticated optical circuits involving high-visibility classical and quantum interference. Already a number of photonic quantum circuits have been realized for quantum metrology [3,4,10,11,12,13], lithography [6], quantum logic gates [14,15,16,17,18,19,20], and other entangling circuits [21,22,23,24]. However, these demonstrations have relied on large-scale (bulk) optical elements bolted to large optical tables, thereby making them inherently unscalable and confining them to the research laboratory. In addition, many have required the design of sophisticated interferometers to achieve the sub-wavelength stability required for reliable operation.We demonstrated the fundamental building blocks of photonic quantum circuits using silica waveguides on a silicon chip: high visibility (98.5±0.4%) classical interference; high visibility (94.8±0.5%) two photon quantum interference; high fidelity controlled-NOT (CNOT) entangling logic gates (logical basis fidelity F = 94.3 ± 0.2%); and on-chip quantum coherence confirmed by high fidelity (> 92%) generation of a two-photon path entangled state. The monolithic nature of these devices means that the correct phase can be stably realized in what would otherwise be an unstable interferometer, greatly simplifying the task of implementing sophisticated photonic quantum circuits. We fabricated 100's of devices on a single wafer and find that performance across the devices is robust, repeatable and well understood.A typical photonic quantum circuit takes several optical paths or "modes" (some...

Classical boson sampling algorithms with superior performance to near-term experiments

“…The advent of integrated quantum photonics 10 has enabled large, complex, stable and programmable optical circuitry 11,12 , while recent advances in photon generation [13][14][15] and detection 16,17 have also been impressive. The possibility to generate many photons, evolve them under a large linear optical unitary transformation, then detect them, seems feasible, so the role of a boson sampling machine as a rudimentary but legitimate computing device is particularly appealing.…”

Gallium arsenide (GaAs) quantum photonic waveguide circuits

“…A single-qubit can therefore be represented as a superposition of these two states: (1) where the photon is simultaneously present at |10 and |01 paths with respective probabilities of detection being | | 2 and | 2 . The directional coupler (see Fig.3 (a)) is a typical form of integrated beamsplitter and performs a unitary operation of the single-qubit state [11]. Starting with an initial state of |10 for instance, directional coupler rotates it into a superposition state of √ √ , where is the reflectivity or coupling ratio of the coupler (see details in Appendix A).…”

“…Recently, two-photon quantum interference with a visibility of >99%, controlled-NOT quantum gate with a fidelity of 96%, and manipulations of entanglement have been demonstrated in the integrated photonic circuits, based on various platforms such as silica-on-silicon [11][12][13][14][15], laser direct writing silica [17], lithium niobate [18,19] and silicon-on-insulator [20,21], etc. Moreover, IQP would enable on-chip generation, manipulation and detection of quantum states of photons, ultimately required by practical and scalable quantum information processing technologies.…”

“…Utilizing well-developed integration technologies of classical photonics, IQP can shrink quantum experiments from a room-sized optical table onto a coin-sized semiconductor chip, and therefore greatly reduce the footprint of quantum devices and increase the complexity of quantum circuits [5,[11][12][13][14][15][16][17][18][19][20][21]. IQP inherently offers near-perfect mode overlap at an integrated beam splitter for highfidelity quantum interference [15] and subwavelength stability of optical path lengths for highvisibility classical interference [11,14], which are both essential to photonic quantum information processing.…”

Deterministic separation of arbitrary photon pair states in integrated quantum circuits

“…Mapping quantum photonic technologies into an integrated on-chip setting has become an important task for overcoming the severe stability and scalability limitations of bulk-optics implementations. Recent efforts have demonstrated on-chip quantum state generation [4][5][6], manipulation [7][8][9][10][11][12] and detection [13] across numerous material platforms including GaAs [6,11,13], silicon wire [5,12], silica-on-silicon [7,8,10], lithium niobate [14] and borosilicate glass [9].…”