Although Nvidia are not releasing their optical quantum chip until 2026/7, other companies such as Xanadu’s Photonic have one already in production
Photonic quantum computing is a promising approach to building scalable quantum computers using photons (particles of light) as qubits. Unlike other quantum computing platforms that rely on trapped ions, superconducting circuits, or spin qubits, photonic systems leverage the unique properties of light to perform quantum computations. Photonic chips are set to disrupt multiple industries by enabling light-speed computing, ultra-efficient data centers, quantum breakthroughs, and advanced sensing. While challenges remain, the next decade will likely see photonics becoming mainstream, complementing nd eventually surpassing traditional electronics in many applications.
Photonic Qubit Advantage
Low decoherence: Photons do not easily interact with their environment, preserving quantum states longer.
Room-temperature operation: Unlike superconducting qubits, photonic systems don’t require extreme cooling.
High-speed operations: Photons travel at the speed of light, enabling fast quantum gates.
Natural compatibility with quantum communication: Photons are ideal for quantum networking (e.g. quantum internet).
Present Challenges
Difficulty in photon-photon interactions: Photons don’t naturally interact, making two-qubit gates hard to implement.
Loss and detection inefficiencies: Photons can be lost in optical systems, and detectors aren’t perfect.
Qubit Encoding in Photons
Photonic qubits can be encoded in different degrees of freedom:
Polarization qubits: Using horizontal (|H⟩) and vertical (|V⟩) polarization states.
Time-bin qubits: Using early and late time slots (e.g. |0⟩ = early, |1⟩ = late).
Spatial mode qubits: Using different paths in an interferometer.
Frequency qubits: Using different optical frequencies.
B. Single-Qubit GatesSingle-qubit operations are performed using linear optical elements:
Waveplates (for polarization qubits).
Beam splitters (for path-encoded qubits).
Phase shifters (for introducing relative phases).
Since photons don’t interact directly, two-qubit gates require
Nonlinear optical effects (weak and hard to control). Measurement-induced nonlinearity (e.g. using fusion gates or KLM protocol). D. Photon Sources. Post-selection: Discarding unsuccessful operations (reduces efficiency).
Reliable quantum computing requires
Single photon sources (e.g. quantum dots, NV centers, SPDC crystals).Indistinguishable photons (critical for interference based gates).
E. Photon Detection
Superconducting nanowire single-photon detectors (SNSPDs): High efficiency (~90%). Transition-edge sensors (TES): Near-perfect detection but slower.Silicon photomultipliers (SiPMs): Lower cost but higher noise.
Approaches to Photonic Quantum Computing
Linear Optical Quantum Computing (LOQC):
Probabilistic gates with post-selection. Requires large overhead but is theoretically scalable. Measurement Based Quantum Computing (MBQC)
Uses cluster states (entangled states of many photons). Computation proceeds via single-qubit measurements. Combines photons with matter qubits (e.g. atoms, quantum dots). Enables deterministic gates via photon-atom interactions.
Quantum Networking
Photons are ideal for quantum repeaters and long-distance QKD (quantum key distribution). D. Near-Term Applications.
Quantum simulations (chemistry, optimization).
Machine learning (quantum-enhanced algorithms).
Cryptanalysis (breaking RSA with Shor’s algorithm in the future).