Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Quantum Information and Measurement (QIM)

Quantum algorithms on a four-qubit photonic controlled-shift gate

Joseph Ho, Raj B. Patel, Timothy C. Ralph, Geoff J. Pryde

Published Jan 1, 2019• 0 citations
Publisher

Abstract

We implement a four-qubit controlled-shift gate leveraging photon entanglement in extended Hilbert spaces and observe Psuccess = 0.25. This enables our demonstration of a DQC1 protocol and the quantum phase estimation algorithm featuring a multi-qubit unitary.
DOI
10.1364/qim.2019.f5a.41

Related papers

Implementation of a quantum Fredkin gate using an entanglement resource

Franck Ferreyrol, Timothy C. Ralph, Geoff J. Pryde

Summary form only given. Photonic qubit logic provides flexible, low noise scheme for quantum information processing. However, implementation of increasing scale requires numbers of resources beyond what is readily available. A recent demonstration [1] has shown how to add a control operation to existing unitary transformations, providing a practical method for moving to medium-scale quantum circuits. Here we use the entanglement-based version of this scheme to implement a complex quantum gate - the Fredkin, or 3-qubit swap gate - with significantly less resources than its decomposition into a 2-qubit gate array.In the technique proposed in [1], the Hilbert space is expended in order to have a four-level system for each qubit. Each system is composed of a qubit sub-system on which the target operation acts, and a second qubit sub-system, which remains unaffected. The control is added by gates that switch between the different subsystems according to the control qubit. Despite its conceptual simplicity, this technique still uses too many gates for practical implementations with current photonic technology. A more feasible way is a version that replaces the gates with pre-existing entanglement between the gates with qubit system and the second subsystem. The experiment is based on four possible photon pairs -called x, o, s and e - with photons either only in x and e, leading to the swapping, or only in o and s, leading to no swapping (Fig. 1). Each qubit is encoded twice and the two last modes are only used for triggering. The coincidences and the polarization beam splitter on two first mode ensure that the possibilities for the origin of the photons are linked to the state of the control qubit.The four possible photon pairs are encoding in the polarization mode coming from two polarization entangling down-conversion crystals. One crystal give a photon pair either in modes x or o and the second one a pair in mode s or e . We then separate spatially the polarization mode using beam displacer or Sagnac interferometers to preserve the phase stability (Fig . 2) . From the simulation we expect a fidelity around 85% for the truth table.

Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)•May 1, 2013•2 citations

Implementing a Multi-Qubit Quantum Phase Gate Encoded by Photonic Qubit

Pei-Min Lu, Song Jie, Yan Xia

A protocol is proposed to implement a three-qubit phase gate for photonic qubits in a three-mode cavity. The idea can be extended to directly implement a N-qubit phase gate. We also show that the interaction time remains unchanged with the increasing number of qubits. In addition, the influence of cavity decay and atomic spontaneous emission on the gate fidelity and photon loss probability is also discussed by numerical calculation.

Chinese Physics Letters•Mar 1, 2010•7 citations

Quantum simulation of an exciton-transfer Hamiltonian on a silicon photonic circuit

Antonio Andreas Gentile

An integrated silicon quantum photonic device, capable of implementing non-compiled controlled unitary operations (CUs), is performing a new variational protocol for searching the ground state of an exciton-transfer Hamiltonian in chlorophyll. This protocol only requires single-qubit measurements ―amenable for scalable quantum photonic approaches ― independently from the dimension of the Hamiltonian system. A maximally path-entangled state, |0>C|0>T +|1>C|0>T, is created on chip through the SFWM effect in silicon waveguides. Then, the target qubit state (with subscript “T”) is expanded into a four-dimensional space and evolved according to two separate unitary operations, i.e. I (identity) and an arbitrary U∈SU(2), ended with a path-information erasure process. This yields a non-compiled “CU” operation, controlled by the control qubit (with subscript “C”) as |0>C ⊗I|φ>T +|1>C⊗U|φ>T. In this experiment, an exciton-transfer Hamiltonian in chlorophyll is properly mapped as U onto our circuit’s parameters. Both state preparation and CU operations are implemented using thermo-optic phase shifting heaters. Our new protocol draws on the eigenstate-generation features of the Iterative Phase Estimation Algorithm (IPEA), and relies on 1-qubit state-tomography performed on the C-qubit alone, to infer properties of the Hamiltonian. The protocol proposes a variational search of the ground state in the Hilbert space spanned by U’s eigenstates, combining quantum measurements and a classical update scheme for the trial T-states that are prepared and evolved in the quantum circuit at each step of the algorithm. The search is guided by effectively minimizing an objective function Fobj=-αP+βE. Only when the input T-qubit is an eigenstate of U, the purity (P) of the output C-qubit |0> + eiφ|1>is 1, and in this case, eigenphase φprovides an estimator for |φ>T's eigenvalue (E). The on-chip implementation granted a robust, reconfigurable setup for our variational search algorithm: within less than 10 steps, we were able to achieve 99.8% fidelity of the final T-state with the ground-state of the implemented Hamiltonian. Under reasonable assumptions, these preliminary results may pave the way towards a scalable quantum-simulation approach for the ground-state problem.

•Jan 1, 2016•0 citations

Deterministic Quantum Phase Estimation with Linear Circuit Complexity in a Photonic System

M. Midhuna, Ajay Jayachandran, Kanad Sengupta +2 more

Quantum algorithms solve certain computational problems faster than the best known classical algorithms. Many algorithms, including Shor's for factoring, Grover's for unstructured search, and the HHL for solving linear systems, rely on quantum phase estimation (QPE) as a fundamental subroutine. The QPE protocol proceeds through the initialization of a control register in a uniform superposition, controlled unitary evolution encoding the eigenphase, and a final inverse quantum Fourier transform followed by measurement to extract the phase. Here, we address a special class of unitary operators that frequently appear in quantum Fourier transform-based protocols, cyclic group representations, and periodically evolving quantum systems. We introduce a QPE algorithm that successfully reduces the circuit complexity from $\mathcal{O}(n^2)$ to $\mathcal{O}(n)$ for a special class of unitary operators and implement it on a four-qubit photonic system. The four-qubit system is realised using a photon pair, with two qubits encoded in its polarization degree of freedom and the remaining two in its path modes. In contrast to previous photonic implementations of QPE based on dual-rail encoding and KLM protocol, where controlled operations are inherently probabilistic and thus reduce the overall success probability of phase estimation, our scheme is fully deterministic. Moreover, it is scalable to higher-dimensional unitaries, provided the underlying structure of the unitaries is preserved.

quant-pharXiv:2607.13404•Jul 16, 2026•0 citations

Implementing a Multi-Qubit Quantum Phase Gate Encoded by Photonic Qubit

陆培民, 宋杰, 夏岩

一个协议被建议在一个三模式的洞为 photonic qubits 实现一扇 three-qubit 阶段门。这个想法能被扩大直接实现一扇 N-qubit 阶段门。我们也证明相互作用时间与 qubits 的增加的数字仍然保持未改变。另外，洞腐烂的影响和门忠实和光子损失概率上的原子自发的排放被数字计算也讨论。

Chinese Physics Letters•Jan 1, 2010•0 citations

Implementation of phase gates using single photons

V. Hizhnyakov

Quantum computing algorithms using the quantum Fourier transform require repeated use of a phase shift gate. In the case of qubits using optical photons for operation, this gate can be implemented using single-photon beams focused close to the diffraction limit.

arXiv:2501.05230•Jan 9, 2025•0 citations
Summary form only given. Photonic qubit logic provides flexible, low noise scheme for quantum information processing. However, implementation of increasing scale requires numbers of resources beyond what is readily available. A recent demonstration [1] has shown how to add a control operation to existing unitary transformations, providing a practical method for moving to medium-scale quantum circuits. Here we use the entanglement-based version of this scheme to implement a complex quantum gate - the Fredkin, or 3-qubit swap gate - with significantly less resources than its decomposition into a 2-qubit gate array.In the technique proposed in [1], the Hilbert space is expended in order to have a four-level system for each qubit. Each system is composed of a qubit sub-system on which the target operation acts, and a second qubit sub-system, which remains unaffected. The control is added by gates that switch between the different subsystems according to the control qubit. Despite its conceptual simplicity, this technique still uses too many gates for practical implementations with current photonic technology. A more feasible way is a version that replaces the gates with pre-existing entanglement between the gates with qubit system and the second subsystem. The experiment is based on four possible photon pairs -called x, o, s and e - with photons either only in x and e, leading to the swapping, or only in o and s, leading to no swapping (Fig. 1). Each qubit is encoded twice and the two last modes are only used for triggering. The coincidences and the polarization beam splitter on two first mode ensure that the possibilities for the origin of the photons are linked to the state of the control qubit.The four possible photon pairs are encoding in the polarization mode coming from two polarization entangling down-conversion crystals. One crystal give a photon pair either in modes x or o and the second one a pair in mode s or e . We then separate spatially the polarization mode using beam displacer or Sagnac interferometers to preserve the phase stability (Fig . 2) . From the simulation we expect a fidelity around 85% for the truth table.
An integrated silicon quantum photonic device, capable of implementing non-compiled controlled unitary operations (CUs), is performing a new variational protocol for searching the ground state of an exciton-transfer Hamiltonian in chlorophyll. This protocol only requires single-qubit measurements ―amenable for scalable quantum photonic approaches ― independently from the dimension of the Hamiltonian system. A maximally path-entangled state, |0>C|0>T +|1>C|0>T, is created on chip through the SFWM effect in silicon waveguides. Then, the target qubit state (with subscript “T”) is expanded into a four-dimensional space and evolved according to two separate unitary operations, i.e. I (identity) and an arbitrary U∈SU(2), ended with a path-information erasure process. This yields a non-compiled “CU” operation, controlled by the control qubit (with subscript “C”) as |0>C ⊗I|φ>T +|1>C⊗U|φ>T. In this experiment, an exciton-transfer Hamiltonian in chlorophyll is properly mapped as U onto our circuit’s parameters. Both state preparation and CU operations are implemented using thermo-optic phase shifting heaters. Our new protocol draws on the eigenstate-generation features of the Iterative Phase Estimation Algorithm (IPEA), and relies on 1-qubit state-tomography performed on the C-qubit alone, to infer properties of the Hamiltonian. The protocol proposes a variational search of the ground state in the Hilbert space spanned by U’s eigenstates, combining quantum measurements and a classical update scheme for the trial T-states that are prepared and evolved in the quantum circuit at each step of the algorithm. The search is guided by effectively minimizing an objective function Fobj=-αP+βE. Only when the input T-qubit is an eigenstate of U, the purity (P) of the output C-qubit |0> + eiφ|1>is 1, and in this case, eigenphase φprovides an estimator for |φ>T's eigenvalue (E). The on-chip implementation granted a robust, reconfigurable setup for our variational search algorithm: within less than 10 steps, we were able to achieve 99.8% fidelity of the final T-state with the ground-state of the implemented Hamiltonian. Under reasonable assumptions, these preliminary results may pave the way towards a scalable quantum-simulation approach for the ground-state problem.
Quantum algorithms solve certain computational problems faster than the best known classical algorithms. Many algorithms, including Shor's for factoring, Grover's for unstructured search, and the HHL for solving linear systems, rely on quantum phase estimation (QPE) as a fundamental subroutine. The QPE protocol proceeds through the initialization of a control register in a uniform superposition, controlled unitary evolution encoding the eigenphase, and a final inverse quantum Fourier transform followed by measurement to extract the phase. Here, we address a special class of unitary operators that frequently appear in quantum Fourier transform-based protocols, cyclic group representations, and periodically evolving quantum systems. We introduce a QPE algorithm that successfully reduces the circuit complexity from O(n2)\mathcal{O}(n^2)O(n2) to O(n)\mathcal{O}(n)O(n) for a special class of unitary operators and implement it on a four-qubit photonic system. The four-qubit system is realised using a photon pair, with two qubits encoded in its polarization degree of freedom and the remaining two in its path modes. In contrast to previous photonic implementations of QPE based on dual-rail encoding and KLM protocol, where controlled operations are inherently probabilistic and thus reduce the overall success probability of phase estimation, our scheme is fully deterministic. Moreover, it is scalable to higher-dimensional unitaries, provided the underlying structure of the unitaries is preserved.