Abstract
Quantum integrated photonics requires large-scale linear optical circuitry, and for many applications, it is desirable to have a universally programmable circuit, able to implement an arbitrary unitary transformation on a number of modes. This has been achieved using the Reck scheme, consisting of a network of Mach–Zehnder interferometers containing a variable phase shifter in one path as well as an external phase shifter after each Mach–Zehnder. It subsequently became apparent that with symmetric Mach–Zehnders containing a phase shifter in both paths, the external phase shifters are redundant, resulting in a more compact circuit. The rectangular Clements scheme improves on the Reck scheme in terms of circuit depth, but it has been thought that an external phase-shifter was necessary after each Mach–Zehnder. Here, we show that the Clements scheme can be realized using symmetric Mach–Zehnders, requiring only a small number of external phase-shifters that do not contribute to the depth of the circuit. This will result in a significant saving in the length of these devices, allowing more complex circuits to fit onto a photonic chip, and reducing the propagation losses associated with these circuits. We also discuss how similar savings can be made to alternative schemes, which have robustness to imbalanced beam-splitters.
Highlights
Optical quantum computing requires interferometric circuits to process quantum states of light.1,2 In particular, integrated photonic circuits comprising networks of Mach–Zehnder interferometers (MZIs) have emerged as a compact and versatile solution for realizing reconfigurable linear optics,3 with applications to linear optical quantum computing,4–6 boson sampling,7–10 high-dimensional encodings,11,12 quantum simulation,13,14 photonic neural networks,15 and optical field-programmable gate array (FPGAs).16,17 Often, universal reconfigurability is essential or at least desirable in the sense that a device can be programmed to realize any unitary transformation between the input and output modes
Using symmetric MZI (sMZI) implies that the circuit length taken up by phaseshifters is approximately halved compared to asymmetric MZI (aMZI)
The saving in length comes at the expense of a somewhat more complicated control strategy: multiple phase-shifters need to be tuned together to configure the parameters of an sMZI, which could negatively impact their precision
Summary
Optical quantum computing requires interferometric circuits to process quantum states of light. In particular, integrated photonic circuits comprising networks of Mach–Zehnder interferometers (MZIs) have emerged as a compact and versatile solution for realizing reconfigurable linear optics, with applications to linear optical quantum computing, boson sampling, high-dimensional encodings, quantum simulation, photonic neural networks, and optical field-programmable gate array (FPGAs). Often, universal reconfigurability is essential or at least desirable in the sense that a device can be programmed to realize any unitary transformation between the input and output modes. Universal reconfigurability is essential or at least desirable in the sense that a device can be programmed to realize any unitary transformation between the input and output modes This can be achieved using the architecture by Reck et al (the Reck scheme), shown, a triangular mesh with each unit cell comprising a variable beam-splitter and a variable phase-shifter. We subsequently show that the additional mid-circuit phase-shifts can be moved to otherwise vacant positions at the edge of the circuit, where they do not contribute to the overall length This approximately halves the contribution of the phase-shifters to the length of a circuit, down to at most external phase-shifters at the inputs and outputs of the circuit, which are not required for some applications.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
