Quantum Computing

Oxford Instruments provide the advanced dilution refrigerator systems necessary for both early-stage qubit research and development and scaling towards commercial quantum computing solutions. Dilution refrigerators, which provide millikelvin temperatures, are a critical part of the infrastructure requirements for the current generation of solid-state quantum computers. This ultra-cold environment is required to access the quantum state, and ensure that the qubit coherence time can be maintained for a sufficient period for practical computation.

The energy level separation of the qubit 1’s and 0’s at the low temperatures required for operation are typically in the GHz frequency range, with carefully shaped nanosecond pulses required to control the computational operations. Coaxial lines bring these signals back to the room temperature environment which causes a heat load on the cryogenic system. Heat dissipating hardware required for signal conditioning, such as amplifiers, attenuators and filters add additional heat load, requiring further increases in cooling power. As these systems scale, there are challenges both in terms of physical space for the cold electronics, and cooling capacity to support their operation.

An example experiment configuration is shown for characterisation of superconducting qubits. Input lines are highly attenuated at each stage to reduce the impact of thermal noise from block body radiation. Amplifiers are installed on the output lines at low temperature to ensure sufficient signal amplification, and circulators are required to limit the impact on the sample from amplifier noise, whilst ensuring minimal attenuation of the output signal. 

The ProteoxMX system provides a modular platform for qubit development and qubit scale-up, enabling the system to be customised for the experiment configuration. The Secondary Insert, combined with Oxford Instruments' cold electronics integration experience enable a full experiment setup to be factory-installed directly onto a modular, self-supporting platform. This customisable line-of-sight access port maximises available space and allows scaling to high qubit counts with capacity for 128 coaxial lines per insert, and system cooling power of up to 12 µW at 20 mK.

The Proteox platform provides a scalable architecture, allowing for increased secondary insert counts and increased cooling capacity to meet the demands of future quantum hardware.

 

Experimental set-up for characterisation of superconducting qubits

Oxford Instruments measurement-ready cold electronics integration for qubit applications

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Oxford Instruments offer reliable and state of device fabrication solutions for the various approaches in hardware platforms to realise quantum computers.  Our solutions are tailored to enable the development of robust qubits with long-lived quantum states and with possible execution of rapidly addressable quantum gates. In addition, our solutions provide reliable pathways towards scaling up to fabricate a large set of interacting qubits and control elements.  

There are several approaches and materials platforms to achieve highly scalable quantum circuits. Superconducting quantum circuits and trapped ion approaches are a couple of the leading technologies to real-world applications. There are, however, several technical challenges in scaling either trapped ion or superconducting quantum computers which has led to the exploration of a wide variety of other approaches for creating qubits, such as photonic quantum computing using integrated photonics approaches; high-temperature qubits, such as diamond NV centres; semiconductor-based spin qubits; exotic topologically protected qubits or Hybrid approaches which take advantage of all these elements. These technologies are slightly lower on the technology-readiness scale but rapidly evolving with new and improved developments every day.

Oxford Instruments offer fabrications solutions to several of the leading approaches to qubit fabrication:

• Atomic Layer Deposition (ALD)
  • Of superconducting materials for Qubits, Quantum Circuits, Microwave resonators, and single-photon detectors, such as NbN and TiN and more
  • Of dielectrics (such as Al₂O₃, AlN and TaN) for tunnel barriers in Josephson Junctions
  • Al₂O₃ as a passivation layer for the fabrication of optical components in diamond (microcavities, nanobeams, waveguides etc)
• Superconducting metal etching, e.g. Nb, Ta, Al, TiN
• PECVD and ICP CVD
  • Of SiNx with low hydrogen content for low-loss waveguides
  • SiNx used as a hard mask for diamond structuring
• Smooth sidewall etching via Bosch or cryo etch of SiNx, InP and GaAs for integrated photonic components in optical quantum technologies
• Reactive Ion Etching (RIE) for smooth, low damage diamond thinning with O termination to further protect NV centres.
• Deep Si Etch for TSV to enable 3D integration of Quantum circuits

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As an alternative approach to solid-state quantum computing, photonic quantum computing uses individual photons as qubits within an optical system. This approach presents significant advantages, in that coherence times for entangled photons are long-lasting and can provide an increase in useful computation time of the system. As an additional advantage, it is not necessary to scale the photons to achieve greater qubit counts. Each photon has multiple modes, such as frequency, polarisation, time and location, all of which can be entangled and encoded simultaneously.

The challenges for photonic quantum computing include loss rates at interfaces and within photonic elements, and sensors sensitive enough to detect single photons. Scalability of the devices is also a challenge, with requirements for an increasing number of single-photon detectors as the number of photons within the system is increased.

Oxford Instruments offer the world's more sensitive cameras for the detection of single photons and entanglement. These are used to superb effect in systems where spatially correlated photons, incident on an imaging array, need to be detected with superb levels of discrimination and confidence, ultimately yielding accelerated measurement throughout.

• Arrays up to 1 Megapixel: Massively parallel detection of quantum correlations, yielding huge efficiency gains.
• Detect > 90% of single photons: Single-photon sensitivity and > 90% QE means the vast majority of incident photon events will be detected and registered.
• Discriminate correlated photons: Low spurious noise combined with -100 °C sensor cooling means false positives are minimized, significantly enhancing the statistics of detection.
• High counting rates: more than 50 fps (100’s fps with sub-regions) for enhanced counting rates and higher measurement rates.
• Bi-photons detection: superb charge transfer efficiency offers confident discrimination of bi-photons in adjacent pixels.
• High QE > 700nm: superb sensitivity into the NIR range enables optional use of photon wavelengths that are spectrally separate from residual fluorescence of optics

Real-time Imaging of Quantum Entanglement

Quantum entanglement occurs when two particles remain connected, even over large distances, so that actions performed on one particle have an effect on the other. The Zeilinger group, University of Vienna, have used an Andor ICCD camera to demonstrate that the detector is fast and sensitive enough to image in real-time the effect of the measurement of one photon on its entangled partner.

Additionally, the use of the ICCD camera allowed the group to demonstrate the high flexibility of the setup in creating any desired spatial-mode entanglement, which suggests as well that visual imaging in quantum optics not only provides a better intuitive understanding of entanglement but will improve applications of quantum science.

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