Embodiments of the present disclosure include optical transmitters and transceivers with improved reliability. In some embodiments, the optical transmitters are used in network devices, such as in conjunction with a network switch. In one embodiment, lasers are operated at low power to improve reliability and power consumption. The output of the laser may be modulated by a non-direct modulator and received by integrated optical components, such as a modulator and/or multiplexer. The output of the optical components may be amplified by a semiconductor optical amplifier (SOA). Various advantageous configurations of lasers, optical components, and SOAs are disclosed. In some embodiments, SOAs are configured as part of a pluggable optical communication module, for example.

Quantum repeater systems and apparatus for quantum communication. In one aspect, a system includes a quantum signal receiver configured to receive a quantum field signal; a quantum signal converter configured to: sample quantum analog signals from a quantum field signal received by the quantum signal receiver; encode sampled quantum analog signals as corresponding digital quantum information in one or more qudits, comprising applying a hybrid analog-digital encoding operation to each quantum analog signal and a qudit in an initial state; decode digital quantum information stored in the one or more qudits as a recovered quantum field signal, comprising applying a hybrid digital-analog decoding operation to each qudit and a quantum analog register in an initial state; a quantum memory comprising qudits and configured to store digital quantum information encoded by the quantum signal converter; and a quantum signal transmitter configured to transmit the recovered quantum field signal.

Quantum repeater systems and apparatus for quantum communication. In one aspect, a system includes a quantum signal receiver configured to receive a quantum field signal; a quantum signal converter configured to: sample quantum analog signals from a quantum field signal received by the quantum signal receiver; encode sampled quantum analog signals as corresponding digital quantum information in one or more qudits, comprising applying a hybrid analog-digital encoding operation to each quantum analog signal and a qudit in an initial state; decode digital quantum information stored in the one or more qudits as a recovered quantum field signal, comprising applying a hybrid digital-analog decoding operation to each qudit and a quantum analog register in an initial state; a quantum memory comprising qudits and configured to store digital quantum information encoded by the quantum signal converter; and a quantum signal transmitter configured to transmit the recovered quantum field signal.

Techniques disclosed herein relate to photon sources with high spectral purity and high brightness. In one embodiment, a photon-pair source includes a pump waveguide, a first resonator coupled to the pump waveguide to couple pump photons from the pump waveguide into the first resonator, a second resonator coupled to the first resonator, and an output waveguide coupled to the second resonator. The second resonator is configured to convert the pump photons into photon pairs. The second resonator and the first resonator are configured to cause a coupling-induced resonance splitting in the second resonator or the first resonator. The second resonator and the output waveguide are configured to couple the photon pairs from the second resonator into the output waveguide. In some embodiments, the photo-pair source includes one or more tuners for tuning at least one of the first resonator or the second resonator.

Techniques disclosed herein relate to photon sources with high spectral purity and high brightness. In one embodiment, a photon-pair source includes a pump waveguide, a first resonator coupled to the pump waveguide to couple pump photons from the pump waveguide into the first resonator, a second resonator coupled to the first resonator, and an output waveguide coupled to the second resonator. The second resonator is configured to convert the pump photons into photon pairs. The second resonator and the first resonator are configured to cause a coupling-induced resonance splitting in the second resonator or the first resonator. The second resonator and the output waveguide are configured to couple the photon pairs from the second resonator into the output waveguide. In some embodiments, the photo-pair source includes one or more tuners for tuning at least one of the first resonator or the second resonator.

A method for compiling a quantum circuit on a trapped-ion quantum processor includes: obtaining a quantum circuit containing a first predetermined category of two-qubit quantum gates, and/or one-qubit quantum gates; a separation of the quantum circuit into local layers, and entangling layers; compiling the local layers; compiling the entangling layers, separate from the step of compiling the local layers, transforming the quantum gates of those entangling layers so that they contain only collective or entangling N-qubit quantum gates of a third predetermined category, one-qubit quantum gates of a fourth predetermined category; and a step of grouping together the compiled local layers and the compiled entangling layers into a compiled quantum circuit.

A method for compiling a quantum circuit on a trapped-ion quantum processor includes: obtaining a quantum circuit containing a first predetermined category of two-qubit quantum gates, and/or one-qubit quantum gates; a separation of the quantum circuit into local layers, and entangling layers; compiling the local layers; compiling the entangling layers, separate from the step of compiling the local layers, transforming the quantum gates of those entangling layers so that they contain only collective or entangling N-qubit quantum gates of a third predetermined category, one-qubit quantum gates of a fourth predetermined category; and a step of grouping together the compiled local layers and the compiled entangling layers into a compiled quantum circuit.

A random-number generation unit (301) generates a random bit string. A light-source control unit (302) generates as transmission signal, using a light source, light pulses each of which corresponds to each bit value in the random bit string generated by the random-number generation unit, and emits the light pulses to a reception apparatus. A transmission-side information acquisition unit (305) acquires from a light-source measurement apparatus which has measured the light pulses and has estimated a physical characteristic, the physical characteristic, and acquires from the reception apparatus, a signal reception result of the transmission signal. A transmission-side information generation unit (303) generates a secret key, using the random bit string, the physical characteristic, and the signal reception result.

A random-number generation unit (301) generates a random bit string. A light-source control unit (302) generates as transmission signal, using a light source, light pulses each of which corresponds to each bit value in the random bit string generated by the random-number generation unit, and emits the light pulses to a reception apparatus. A transmission-side information acquisition unit (305) acquires from a light-source measurement apparatus which has measured the light pulses and has estimated a physical characteristic, the physical characteristic, and acquires from the reception apparatus, a signal reception result of the transmission signal. A transmission-side information generation unit (303) generates a secret key, using the random bit string, the physical characteristic, and the signal reception result.

An optical transmitter for quantum key distribution includes a plurality of spatially separated light sources configured to emit a light signal with the same wavelength. Each light source emits a light signal with a unique encoding. A beam combiner receives the light signals from the plurality of light sources and combines the received light signals into a combined light signal. A spatial filter is optically coupled to the beam combiner and includes an aperture that receives the combined light signal and emits a filtered light signal. The aperture has an aperture diameter less than or equal to the specified wavelength. A collimator is optically coupled to the spatial filter and receives the filtered light signal and emits a collimated light signal. An output aperture receives the collimated light signal and outputs the collimated light signal as an output light signal towards an optical receiver.