Quantum Physics

High-speed, thin-film lithium niobate quantum processors powered by quantum emitters—progressive quantum leaps

Versatile photonic quantum figuring designs require photonic handling gadgets. Such stages depend on low-misfortune, fast, reconfigurable circuits and close, deterministic asset state generators. An integrated photonic platform based on thin-film lithium niobate was developed by Patrik Sund and a group of researchers at the center of hybrid quantum networks at the University of Copenhagen and the University of Münster and published in Science Advances. Using quantum dots in nanophotonic waveguides, the researchers integrated the platform with deterministic solid-state single photon sources.

They experimentally realized a variety of important photonic quantum information processing functionalities on high-speed circuits and processed the generated photons in low-loss circuits at speeds of several gigahertz, with the essential properties necessary to construct a universal four-mode photonic circuit. The outcomes represent a promising direction in the improvement of versatile quantum advancements by blending coordinated photonics with strong-state deterministic photon sources.

Quantum hardware is now able to compete with and even surpass the capabilities of classical supercomputers thanks to advancements in integrated photonics and quantum technologies over the past few years. However, it is challenging to create fault-tolerant quantum technologies and scale up quantum system regulation for a variety of practical applications.

For quantum computing and simulation experiments, photonics offers a promising platform for unlocking scalable quantum hardware for long-range quantum networks with interconnections among multiple quantum devices and photonic circuits. The excellent photonic states and the quick, low-misfortune programmable circuits underlie the focal thought of photonic quantum innovations to course and handle applications. In order to create on-demand single-photon sources, solid-state quantum emitters like quantum dots have recently been developed as near-ideal, high-efficiency sources of indistinguishable photons.

A description of the platform. A and B) Schematics of the designed waveguide geometry, tailored for the quantum emitter’s 940 nm operation wavelengths, for (A) multimode straight waveguides and (B) SM waveguides utilized in bends and directional couplers The fundamental TE waveguide mode’s field intensity is arranged in a color-coded manner. C) The fabricated grating couplers’ measured coupling efficiency as a function of the input laser wavelength, with a peak efficiency of 3.4 dB. An image of the coupler from a scanning electron micrograph is shown in the inset. D) An image of an electrically tunable MZI taken with an optical microscope E) Schematic of the cross-section of the electro-optic stage shifter (F) Tweak the data transfer capacity of the MZI estimated with a VNA. The data indicate a cutoff of three decibels around 6.5 GHz. Inset: schematic of the arrangement utilized in the estimation. Credit: Science is moving forward. DOI: 10.1126/sciadv.adg7268

Photonic quantum data handling
During this review, Sund and partners zeroed in on single-precious stone lithium niobate flimsy movies fortified on a silica-protecting substrate as a promising stage because of their solid electrical-optical properties, high straightforwardness, and high file difference to frame coordinated circuits. The materials’ wide transparency range made them compatible with a wide range of solid-state quantum emitters and allowed them to function at cryogenic temperatures.

The development of multimode lithium niobate on insulator circuits for quantum information processing at the single photon level was first described in this work by the team. By controlling and facilitating the operation of quantum states of light emanating from a quantum dot single-photon source, they were able to accomplish this. To demonstrate important aspects of photonic quantum information processing, like multiphoton interference on a reconfigurable universal unitary circuit, the team injected single photons from a waveguide-integrated quantum dot source into the lithium niobate optical circuit.

Photon handling in multimode rapid coordinated circuits (A) A chip optical image The 4 x 4 universal interferometer is highlighted in orange, and the photon router structure is highlighted in blue. B) Schematic of the experimental setup for active 14-demultiplexing of a QD-generated stream of single photons Using a fiber array, photons are directly coupled into and out of the chip, and their arrival time is recorded using SNSPDs and a time tagger. Quick electrical control is performed by means of a capability generator (FG) associated with the modulators through a test station, where one channel is utilized to exclusively address the MZI in the primary layer and the other channel is parted to drive both MZIs in the subsequent layer in equal measure. (C) The normalized number of photons in each of the four output waveguides over the course of a four-photon sequence D) Associated pulse sequences, shown in insets with the corresponding switching network configurations E) Schematic of the universal four-by-four interferometer’s experimental setup A probe station is used to electrically connect the ten high-speed modulators, which are then driven by a multichannel function generator. F and G): exploratory information (top) and assessed hypothetical (base) crash-free information yield likelihood disseminations while programming the interferometer to carry out a rough stage network (F) and a randomized unitary lattice (G), with assessed measurable loyalties of 96.3 and 95.5%, individually. In terms of the mode indices of the first and second photons, the horizontal index denotes the input configuration, and the color denotes the output configuration. Run lines separate different information setups. Credit: Science Advances (2023). DOI: 10.1126/sciadv.adg7268

Integrated photonic stages
Sund and partners delineated the math used to acknowledge single-mode lithium niobate on separator waveguides. Using electron-beam lithography and argon etching on a lithium niobate film bonded to a silica-on-silicon substrate, they turned the optical circuits into rib waveguides.

Subsequent to drawing them, they clad the waveguides with a hydrogen silsesquioxane layer and optically coupled the photonic coordinated circuits to single-mode filaments for further developed coupling effectiveness and a functioning way to deal with interface quick optical switches and circuits with optical strands. Using a Mach-Zehnder interferometer with directional couplers and an electrically tunable phase shifter, the materials scientists and engineers constructed the electro-optically tunable waveguide circuits. In order to evaluate the capabilities of the constructed photonic integrated circuits, the team put the modulators’ high-speed performance through its paces.

On-chip Hong-Ou-Mandel experiments were used by the researchers to test the platform’s performance for photonic quantum information processing by examining the visibility of multiphoton quantum interference during photonic quantum information processing. The materials researchers created single photons by utilizing a self-collected indium arsenide quantum spot implanted in a photonic and electronic nanostructure.

The device had a heterodiode for electrical noise suppression and emission wavelength tuning, as well as a shallow-etched waveguide grating and a single-sided photonic crystal waveguide for efficient photon generation. Using an off-chip demultiplexer to separate pairs of consecutive photons, the researchers created a two-photon input state from the quantum dot’s stream of single photons, allowing the photons to arrive at the chip simultaneously. For the purpose of detecting coincidences, they then directed the photons toward single-photon detectors.

measurement of the loss of propagation in the waveguide an optical magnifying instrument picture showing the arrangement of twistings utilized for assessing the engendering loss of LNOI waveguides. b The four spirals’ measured transmission was plotted on a dB scale (blue squares). Normalized to the transmission of a reference device with just two grating couplers connected by a short waveguide, the data are processed. On the log scale, the experimental data were fitted linearly to the red line. Credit: Science is moving forward. DOI: Integrated single-photon router: 10.1126/sciadv.adg7268

Because they can be installed with multiple modes for multiplexing schemes in near-deterministic functions, fast photon routers are important in photonic quantum computing. In order to cut costs in photonic quantum computing architectures, Sund and colleagues utilized deterministic quantum emitters by rotating streams of emitted photons.

The exploration group incorporated quick stage shifters on lithium niobate stages and showed on-chip photon switches for quantum-dab-produced photons. Three fast electro-optic Mach Zehnder interferometer switches cascaded in a tree-shaped matrix network made up the experimental setup’s demultiplexer. On the insulator platform, lithium niobate’s promising potential to direct quantum dot-produced photons was demonstrated throughout the entire experimental circuit.

Schematics of full exploratory arrangements A. Schematic of the trial arrangement used to perform estimations of two-photon impedance in two-mode and four-mode interferometers Optics: A quantum dot (QD) single-photon source is driven by a pulsed laser at 72 MHz to produce a stream of single photons that are sent to a two-mode demultiplexer with an electro-optic modulator (EOM) and a polarizing beamsplitter (PBS). After that, the photons are split up by the demultiplexer into two modes, one of which is delayed so that the photons are in sync. After that, the synchronized photons are coupled to a fiber array (FA) and sent to the chip through on-chip grating couplers and a fiber array (FA). Superconducting nanowire single-photon detectors (SNSPDs) are used to find the output photons, and a time tagger (TT) records the arrival times. Electronics: Using a beamsplitter, a portion of the pulsed laser is split off, and a photodiode (PD) is used to measure it. The subsequent clock signal is used to set off the EOM. A synchronization signal is sent to the TT to enable coincidence measurements between the control signal and single-photon detection events. An AC signal is used to drive the modulators by a function generator (FG). B. Schematic of the experimental setup for active 14 demultiplexing of a quantum dot (QD) single-photon source’s stream of single photons Optics: A QD single-photon source is driven by a pulsed laser at 72 MHz, resulting in a stream of single photons. The flood of photons is steered straightforwardly into the chip through a fiber cluster (FA) and on-chip grinding couplers, and the resultant photons are extricated from various grinding couplers with a similar fiber exhibit. Superconducting nanowire single-photon detectors (SNSPDs) are used to find these output photons, and a time tagger (TT) records their arrival times. Elecronics: Using a beamsplitter, a portion of the pulsed laser is split off, and a photodiode (PD) is used to measure it. A field-programmable gate array (FPGA) is used to downsample a portion of this clock signal so that it can be used to trigger a square waveform on an arbitrary waveform generator (AWG) with a repetition rate of less than 5 MHz. A function generator (FG) that drives the modulators in an on-chip demultiplexer structure is triggered by this 5 MHz signal. A synchronization signal from the FG and the other piece of the clock signal from the PD are sent into a period tagger to empower happenstance location between the information photon clock signal, the electronic control signal, and the single-photon identification occasions. Credit: Science is moving forward. DOI: 10.1126/sciadv.adg7268

Universal four-mode interferometer Multimode quantum photonic interferometers with programmable components are essential for implementing photonic quantum technologies’ core functionalities, such as fusion measurements and multiphoton gates, in order to create circuits for analog quantum simulation or quantum computation experiments. For this kind of experiment, the team looked into using quantum dot-lithium niobate on insulator platforms and built an interferometer out of a network of six Mach Zehnder interferometers and ten phase modulators. The scientists then compared the theoretical predictions to the measured distributions from the experimental data.

Along these lines, Patrik Sund and partners showed the commitment of lithium niobate on separator stages to handle photons from arising strong-state deterministic sources. For scalable quantum technologies, further optimization of the platform is possible.

The group proposes utilizing a cladding with a higher refractive index during the trials for improved results. A way to scale up quantum photonic technologies beyond photonic nanostructures and achieve fault-tolerant photonic quantum computing on a large scale is provided by high-speed lithium niobate on insulator quantum processors.

More information: Patrik I. Sund et al, High-speed thin-film lithium niobate quantum processor driven by a solid-state quantum emitter, Science Advances (2023). DOI: 10.1126/sciadv.adg7268

Han-Sen Zhong et al, Quantum computational advantage using photons, Science (2021). DOI: 10.1126/science.abe8770

Topic : Article