One of the most significant challenges in quantum computing is the variability in implementing quantum algorithms across different chips. In this work, we present a Hadamard photonic gate based on the quantum Fourier transform, which superimposes several numbers encoded in the classical domain. We recognize that various mathematical operations - such as addition, subtraction, multiplication, division, and other complex calculations - are typically processed separately for each nth number in classical computers. This approach consumes considerable memory space and results in slower processing speeds as the number of bits increases. With the advancements provided in this work, we can eliminate the need for multiple memory spaces, allowing all numbers to be processed simultaneously in a single computation step. This is a key reason why quantum computers are significantly faster than their classical counterparts. Notably, as the number of bits increases, the number of processes remains consistent, enabling the same operations to be performed without requiring additional memory capacity. We have designed this algorithm using an optical integrated circuit that includes a silicon dioxide waveguide in an air bed, operating at a wavelength of 1.55 µm. Importantly, this circuit can not only be implemented independently on hybrid chips but also integrated into quantum monolithic chips based on Silicon Dioxide-Air optical waveguides as a key component of the overall structure.
One of the most significant challenges in quantum computing is the variability in implementing quantum algorithms across different chips. In this work, we present a Hadamard photonic gate based on the quantum Fourier transform, which superimposes several numbers encoded in the classical domain. We recognize that various mathematical operations - such as addition, subtraction, multiplication, division, and other complex calculations - are typically processed separately for each nth number in classical computers. This approach consumes considerable memory space and results in slower processing speeds as the number of bits increases. With the advancements provided in this work, we can eliminate the need for multiple memory spaces, allowing all numbers to be processed simultaneously in a single computation step. This is a key reason why quantum computers are significantly faster than their classical counterparts. Notably, as the number of bits increases, the number of processes remains consistent, enabling the same operations to be performed without requiring additional memory capacity. We have designed this algorithm using an optical integrated circuit that includes a silicon dioxide waveguide in an air bed, operating at a wavelength of 1.55 µm. Importantly, this circuit can not only be implemented independently on hybrid chips but also integrated into quantum monolithic chips based on Silicon Dioxide-Air optical waveguides as a key component of the overall structure.
One of the main challenges in quantum computing is implementing algorithms within quantum optical free-space and integrated circuits. This research focuses on the quantum addition algorithm, derived from the Deutsch-Jozsa algorithm, to advance quantum computing using optical technologies. The developed quantum optical integrated circuit is built on a hybrid substrate with interconnected components on a silicon dioxide base. Qubits and their states are arranged according to the requirements of each quantum algorithm. In the Fourier transform section, qubits act as propagation modes within silicon waveguides, with emitted photons representing the Fourier transform after traveling a distance of π/2. The phase-shifting section consists of two parts: one shifts the phase of incoming photons by π, while the other modulates this shift based on the quantum full adder algorithm. The first employs a photonic crystal for short phase shifts, which are adjusted via impurities in the silicon substrate and controlled by an electro-optic circuit. Additionally, single-mode waveguides made of silicon dioxide and air serve as qubits. By coupling photon amplitudes, a comparator circuit is triggered based on the generated output. Through these integrations, the sum of two quantum numbers can be represented at the output. This underscores the importance of designing and simulating a full adder within quantum optical integrated circuits to address the complexities inherent in quantum computing.
Abstract Integrated quantum photonic circuits are a promising approach to realizing future quantum information processing. To achieve large-scale quantum photonic circuits, as many quantum logic gates as possible are expected to be integrated on chips. This requires quantum logic gates to be as small as possible. Here, we report the implementation of super-compact universal quantum logic gates on silicon photonic chips by inverse design. The sizes for the fabricated optical controlled-NOT gate and single-qubit gates (Hadamard gate) on the chip are about one vacuum wavelength, which are the smallest optical quantum gates ever verified in the world. The quantum circuit by these cascaded fundamental gates is shrunk several orders compared to those previous quantum photonic circuits that perform arbitrary quantum processing. Our study paves the way for the realization of large-scale quantum photonic chips with integrated sources for practical quantum information processes.
Controlling and programming quantum devices to process quantum information by the unit of qudit shows great potential to enhance the capabilities of qubit-based quantum technologies. Here, we report a programmable qudit-based quantum processor in silicon-photonic integrated circuits and demonstrate its enhancement of quantum computational parallelism. The processor monolithically integrates all the key functionalities and capabilities of initialisation, manipulation, and measurement of the two-ququart states and multi-value quantum-controlled logic gates with high-level fidelities. We implemented the basic quantum Fourier transform algorithms to benchmark the enhancement of quantum parallelism using qudits, allowing the implementations of more than one million high-fidelity preparations, operations and projections of qudit states in the processor. Our work shows an integrated quantum technology for qudit-based quantum computing with enhanced capacity, accuracy, and efficiency.
Although practical realisation of a fully functioning quantum computer is still a long way off, recent progress both experimentally and theoretically is paving the way for possible implementations. One of the leading approaches is quantum optics, where photons are used as carriers of quantum information, and are manipulated in both linear and non-linear optical circuits. More recently, advances in integrated quantum photonics are enabling the realisation of compact and stable quantum gates and circuits. This approach provides routes to enhancing the complexity of quantum optic experiments, and ultimately towards the development of advanced quantum technologies. This study presents an overview of recent developments in the field of integrated waveguide quantum circuits. Key building blocks required for the realisation of quantum circuits are presented, and a rudimentary version of Shor's quantum factoring algorithm is demonstrated. Planar waveguide quantum circuits provide a high-performance platform from which quantum technologies and experimental quantum physics using single photons can be developed, and a new generation of quantum information and computing devices can be monolithically integrated onto a single optical chip.
Optical chips for quantum photonics are cutting-edge technology, merging photonics and quantum mechanics to manipulate light at the quantum level. These chips are crucial for advancing quantum computing, secure communication, and precision sensing by integrating photonic components such as waveguides, beam splitters, and detectors to manipulate single photons, the fundamental carriers of quantum information. Key advancements in optical chips include low-loss waveguides, efficient single-photon sources, and high-fidelity quantum gates, all essential for scalable quantum circuits. Integrating these circuits on a chip offers significant advantages in miniaturization, stability, and reproducibility over traditional bulk optics setups. Recent breakthroughs in materials science and nanofabrication have propelled the field forward, enabling the production of chips with higher precision and lower defect rates. Silicon photonics, in particular, has become a prominent platform due to its compatibility with existing semiconductor manufacturing processes, facilitating the integration of quantum photonic circuits with classical electronic systems. Here, we share our vision of the future of optical chips for quantum photonics, which hold promise for various applications. In quantum computing, they enable the development of compact and scalable quantum processors. In communication, they provide the foundation for ultra-secure quantum networks through quantum key distribution. In sensing, they allow for high-precision measurements that surpass classical limits. As research progresses, optical chips are expected to play a critical role in realizing the full potential of quantum technologies.
Controlling and programming quantum devices to process quantum information by the unit of qudit provides the possibilities for noise-resilient quantum communications, delicate quantum molecular simulations, and efficient quantum computations, showing great potential to enhance the capabilities of qubit-based quantum technologies. Here, we report a programmable high-dimensional quantum processor in a silicon-photonic in-tegrated circuit, which monolithically integrates all the key functionalities and capabilities of initialisation, manipulation, and measurement of the two quantum quart (ququart) states, and demonstrate its enhancement of quantum computational paral-lelism. By reprogramming the processor, we implemented the basic quantum Fourier transform algorithms, all in quaternary, to benchmark the enhancement of quantum parallelism using qudits. The monolithic integration and high programmability have allowed the implementations of more than one million high-fidelity preparations, operations and projections of qudit states in the processor. Our work shows an integrated photonic quantum technology for qudit-based quantum computing with enhanced capacity, accuracy, and efficiency, which could lead to the acceleration of building a large-scale Quantum computer.