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In-grown diamond color centers with narrow inhomogeneous spectral distributions

Summary

We characterize silicon vacancies in a bulk diamond sample grown at MIT Lincoln Laboratory. The measured narrow, inhomogeneous spectral distribution indicates that they will be useful for implementing scalable quantum networks.
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Summary

We characterize silicon vacancies in a bulk diamond sample grown at MIT Lincoln Laboratory. The measured narrow, inhomogeneous spectral distribution indicates that they will be useful for implementing scalable quantum networks.

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Impact of interconnected architectures on near-term quantum algorithms

Summary

Scaling quantum computers requires interconnected processors; however, the interconnected architecture's effect on computing performance is not well quantified. We assess the impact of architectures on algorithm performance and identify performance benefits relative to interconnect-free architectures.
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Summary

Scaling quantum computers requires interconnected processors; however, the interconnected architecture's effect on computing performance is not well quantified. We assess the impact of architectures on algorithm performance and identify performance benefits relative to interconnect-free architectures.

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High-fidelity control of a strongly coupled electro-nuclear spin-photon interface [e-print]

Summary

Long distance quantum networking requires combining efficient spin-photon interfaces with long-lived local memories. Group-IV color centers in diamond (SiV–, GeV–, and SnV–) are promising candidates for this application, containing an electronic spin-photon interface and dopant nuclear spin memory. Recent work has demonstrated state-of-the-art performance in spin-photon coupling and spin-spin entanglement. However, coupling between the electron and nuclear spins introduces a phase kickback during optical excitation that limits the utility of the nuclear memory. Here, we propose using the large hyperfine coupling of 117SnV– to operate the device at zero magnetic field in a regime where the memory is insensitive to optical excitation. We further demonstrate ground state spin control of a 117SnV– color center integrated in a photonic integrated circuit, showing 97.8% gate fidelity and 2.5 ms coherence time for the memory spin level. This shows the viability of the zero-field protocol for high fidelity operation, and lays the groundwork for building quantum network nodes with 117SnV– devices.
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Summary

Long distance quantum networking requires combining efficient spin-photon interfaces with long-lived local memories. Group-IV color centers in diamond (SiV–, GeV–, and SnV–) are promising candidates for this application, containing an electronic spin-photon interface and dopant nuclear spin memory. Recent work has demonstrated state-of-the-art performance in spin-photon coupling and spin-spin entanglement...

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A cloud-based brain connectivity analysis tool

Summary

With advances in high throughput brain imaging at the cellular and sub-cellular level, there is growing demand for platforms that can support high performance, large-scale brain data processing and analysis. In this paper, we present a novel pipeline that combines Accumulo, D4M, geohashing, and parallel programming to manage large-scale neuron connectivity graphs in a cloud environment. Our brain connectivity graph is represented using vertices (fiber start/end nodes), edges (fiber tracks), and the 3D coordinates of the fiber tracks. For optimal performance, we take the hybrid approach of storing vertices and edges in Accumulo and saving the fiber track 3D coordinates in flat files. Accumulo database operations offer low latency on sparse queries while flat files offer high throughput for storing, querying, and analyzing bulk data. We evaluated our pipeline by using 250 gigabytes of mouse neuron connectivity data. Benchmarking experiments on retrieving vertices and edges from Accumulo demonstrate that we can achieve 1-2 orders of magnitude speedup in retrieval time when compared to the same operation from traditional flat files. The implementation of graph analytics such as Breadth First Search using Accumulo and D4M offers consistent good performance regardless of data size and density, thus is scalable to very large dataset. Indexing of neuron subvolumes is simple and logical with geohashing-based binary tree encoding. This hybrid data management backend is used to drive an interactive web-based 3D graphical user interface, where users can examine the 3D connectivity map in a Google Map-like viewer. Our pipeline is scalable and extensible to other data modalities.
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Summary

With advances in high throughput brain imaging at the cellular and sub-cellular level, there is growing demand for platforms that can support high performance, large-scale brain data processing and analysis. In this paper, we present a novel pipeline that combines Accumulo, D4M, geohashing, and parallel programming to manage large-scale neuron...

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Suppressing relaxation in superconducting qubits by quasiparticle pumping

Summary

Dynamical error suppression techniques are commonly used to improve coherence in quantum systems. They reduce dephasing errors by applying control pulses designed to reverse erroneous coherent evolution driven by environmental noise. However, such methods cannot correct for irreversible processes such as energy relaxation. We investigate a complementary, stochastic approach to reducting errors: instead of deterministically reversing the unwanted qubit evolution, we use control pulses to shape the noise environment dynamically. in the context of superconducting qubits, we implement a pumping sequence to reduce the number of unpaired electrons (quasiparticles) in close proximity to the device. A 70% reduction in the quasiparticle density reesults in a threefold enhancement in qubit relaxation times and a comparable reduction in coherence variablity.
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Summary

Dynamical error suppression techniques are commonly used to improve coherence in quantum systems. They reduce dephasing errors by applying control pulses designed to reverse erroneous coherent evolution driven by environmental noise. However, such methods cannot correct for irreversible processes such as energy relaxation. We investigate a complementary, stochastic approach to...

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The role of master clock stability in quantum information processing

Published in:
npj Quantum Inf., Vol. 2, 8 November 2016, doi:10.1038/npjqi.2016.33.

Summary

Experimentalists seeking to improve the coherent lifetimes of quantum bits have generally focused on mitigating decoherence mechanisms through, for example, improvements to qubit designs and materials, and system isolation from environmental perturbations. In the case of the phase degree of freedom in a quantum superposition, however, the coherence that must be preserved is not solely internal to the qubit, but rather necessarily includes that of the qubit relative to the 'master clock' (e.g., a local oscillator) that governs its control system. In this manuscript, we articulate the impact of instabilities in the master clock on qubit phase coherence and provide tools to calculate the contributions to qubit error arising from these processes. We first connect standard oscillator phase-noise metrics to their corresponding qubit dephasing spectral densities. We then use representative lab-grade and performance-grade oscillator specifications to calculate operational fidelity bounds on trapped-ion and superconducting qubits with relatively slow and fast operation times. We discuss the relevance of these bounds for quantum error correction in contemporary experiments and future large-scale quantum information systems, and consider potential means to improve master clock stability.
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Summary

Experimentalists seeking to improve the coherent lifetimes of quantum bits have generally focused on mitigating decoherence mechanisms through, for example, improvements to qubit designs and materials, and system isolation from environmental perturbations. In the case of the phase degree of freedom in a quantum superposition, however, the coherence that must...

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The flux qubit revisited to enhance coherence and reproducibility

Summary

The scalable application of quantum information science will stand on reproducible and controllable high-coherence quantum bits (qubits). In this work, we revisit the design and fabrication of the superconducting flux qubit, achieving a planar device with broad frequency tunability, strong anharmonicity, high reproducibility, and relaxation times in excess of 40 us at its flux-insensitive point. Qubit relaxation times 1 T across 22 qubits of widely varying designs are consistently matched with a single model involving resonator loss, ohmic charge noise, and 1/f flux noise, a noise source previously considered primarily in the context of dephasing, with temporal variation in 1 T attributed to quasiparticles. We furthermore demonstrate that qubit dephasing at the flux-insensitive point is dominated by residual thermal photons in the readout resonator. The resulting photon shot noise is mitigated using a dynamical decoupling protocol, resulting in T2 ~ 85 us , approximately the 1 2T limit. In addition to realizing a dramatically improved flux qubit, our results uniquely identify photon shot noise as limiting 2 T in contemporary state-of-art qubits based on transverse qubit-resonator interaction.
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Summary

The scalable application of quantum information science will stand on reproducible and controllable high-coherence quantum bits (qubits). In this work, we revisit the design and fabrication of the superconducting flux qubit, achieving a planar device with broad frequency tunability, strong anharmonicity, high reproducibility, and relaxation times in excess of 40...

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Resonance fluorescence from an artificial atom in squeezed vacuum

Published in:
Phys. Rev. X, Vol. 6, No. 3, July-September 2016, 031004.

Summary

We present an experimental realization of resonance fluorescence in squeezed vacuum. We strongly couple microwave-frequency squeezed light to a superconducting artificial atom and detect the resulting fluorescence with high resolution enabled by a broadband traveling-wave parametric amplifier. We investigate the fluorescence spectra in the weak and strong driving regimes, observing up to 3.1 dB of reduction of the fluorescence linewidth below the ordinary vacuum level and a dramatic dependence of the Mollow triplet spectrum on the relative phase of the driving and squeezed vacuum fields. Our results are in excellent agreement with predictions for spectra produced by a two-level atom in squeezed vacuum [Phys. Rev. Lett. 58, 2539 (1987)], demonstrating that resonance fluorescence offers a resource-efficient means to characterize squeezing in cryogenic environments.
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Summary

We present an experimental realization of resonance fluorescence in squeezed vacuum. We strongly couple microwave-frequency squeezed light to a superconducting artificial atom and detect the resulting fluorescence with high resolution enabled by a broadband traveling-wave parametric amplifier. We investigate the fluorescence spectra in the weak and strong driving regimes, observing...

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A near-quantum-limited Josephson traveling-wave parametric amplifier

Published in:
Sci., Vol. 350, No. 6258, 16 October 2015,pp. 307-10.

Summary

Detecting single photon level signals--carriers of both classical and quantum information--is particularly challenging for low-energy microwave frequency excitations. Here we introduce a superconducting amplifier based on a Josephson junction transmission line. Unlike current standing-wave parametric amplifiers, this traveling wave architecture robustly achieves high gain over a bandwidth of several gigahertz with sufficient dynamic range to read out 20 superconducting qubits. To achieve this performance, we introduce a sub-wavelength resonant phase matching technique that enables the creation of nonlinear microwave devices with unique dispersion relations. We benchmark the amplifier with weak measurements, obtaining a high quantum efficiency of 75% (70% including following amplifier noise). With a flexible design based on compact lumped elements, this Josephson amplifier has broad applicability to microwave metrology and quantum optics.
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Summary

Detecting single photon level signals--carriers of both classical and quantum information--is particularly challenging for low-energy microwave frequency excitations. Here we introduce a superconducting amplifier based on a Josephson junction transmission line. Unlike current standing-wave parametric amplifiers, this traveling wave architecture robustly achieves high gain over a bandwidth of several gigahertz...

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Reduction of trapped-ion anomalous heating by in situ surface plasma cleaning

Published in:
Phys. Rev. A, At. Mol. Opt. Phys., Vol. 92, No. 2, 2015, 020302.

Summary

Anomalous motional heating is a major obstacle to scalable quantum information processing with trapped ions. Although the source of this heating is not yet understood, several previous studies suggest that noise due to surface contaminants is the limiting heating mechanism in some instances. We demonstrate an improvement by a factor of 4 in the room-temperature heating rate of a niobium surface electrode trap by in situ plasma cleaning of the trap surface. This surface treatment was performed with a simple homebuilt coil assembly and commercially available matching network and is considerably gentler than other treatments, such as ion milling or laser cleaning, that have previously been shown to improve ion heating rates. We do not see an improvement in the heating rate when the trap is operated at cryogenic temperatures, pointing to a role of thermally activated surface contaminants in motional heating whose activity may freeze out at low temperatures.
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Summary

Anomalous motional heating is a major obstacle to scalable quantum information processing with trapped ions. Although the source of this heating is not yet understood, several previous studies suggest that noise due to surface contaminants is the limiting heating mechanism in some instances. We demonstrate an improvement by a factor...

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