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Advanced Quantum Testbed
Computational Research Division
AQT at Berkeley Lab

srmorgan

June 4, 2020
  • By : srmorgan
  • Quantum Computation & Simulation
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Simulations of RC show better performance as the rate of coherent errors is reduced

Simulations of randomized compiling (RC) show that RC performs better as the error rate of coherent errors is reduced. This is demonstrated in the plot above for single- and multi-qubit random circuits of depth 200 gates (100 cycles of easy/hard gates), where we plot the log of the TVD as a function of the error

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June 4, 2020
  • By : srmorgan
  • Quantum Computation & Simulation
  • 0 Comments

How many randomly compiled circuits do we need to see a benefit from RC?

A valid question to ask is, how many randomly compiled circuits do we need to see a benefit from randomized compiling (RC)? We re-analyzed the random circuit sampling data presented on the RC project page to answer this question. For each circuit depth (K) in which we generated random circuits, we computed the convergence of

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June 4, 2020
  • By : srmorgan
  • Quantum Computation & Simulation
  • 0 Comments

State tomography on a single-qubit

We performed state tomography on a single-qubit at three different points during a random sequence of gates (after 10 gates, after 100 gates, and after 200 gates). This clearly demonstrates the intuition behind randomized compiling (RC): coherent errors can build up as a function of circuit depth, resulting in errors in the bare quantum state

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June 4, 2020
  • By : srmorgan
  • Quantum Computation & Simulation
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Leakage RB

One significant source of error in CR gates, especially when minimizing gate time, is leakage of the quantum state out of the computational subspace, in particular to the second excited state of the control transmon. We have observed and characterized this leakage channel during the CR gate by monitoring directly the second excited states of

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June 4, 2020
  • By : srmorgan
  • Quantum Computation & Simulation
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Observing Target-Qubit Detuning error

To measure the dynamics of the CR gate, we perform Hamiltonian tomography. This experiment involves driving the CR interaction and performing state tomography on the target qubit, thus allowing one to measure the Bloch dynamics of the target qubit, conditioned on the control qubit state. We run this experiment when with the control qubit in

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June 4, 2020
  • By : srmorgan
  • Quantum Computation & Simulation
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Measuring IRB Fluctuations

Randomized Benchmarking (RB) is a standard experiment to quantify the error rate of a quantum gate set. In addition to being relevant for building fault-tolerant quantum computers, reducing two-qubit gate error rates enables the execution of NISQ algorithms with larger-depth. However, environmental drift is a ubiquitous phenomenon in quantum hardware, and it is important to

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April 7, 2020
  • By : srmorgan
  • Quantum Computation & Simulation
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Crosstalk remains a major issue

Crosstalk remains a major issue in the design of microwave drive lines for fast single qubit control. Microwave drive lines for qubit control must be placed sufficiently far from the qubit to limit the qubit-drive line coupling and the resulting decrease in qubit lifetimes via the purcell effect. However, this generally leads to an increase

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February 20, 2020
  • By : srmorgan
  • Quantum Computation & Simulation
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Simulations of two qubit gate dynamics have illustrated well known trade-offs

Simulations of two qubit gate dynamics have illustrated the well known trade-off between coherent and incoherent errors as a function of gate speed. Faster gates are less susceptible to the incoherent error caused by qubit relaxation, while slower gates have lower levels of coherent error due to unwanted interactions with the non-computational states of the

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February 16, 2020
  • By : srmorgan
  • Quantum Computation & Simulation
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Photodetector tested in continuous mode

First acquisition of long trajectories (~ms) to test detector performance when the photon’s arrival time is unknown. The blue trace is the filtered detector response when a weak continuous tone was sent into the detector. Same for the orange trace, except the tone was off so when the trajectory crosses the threshold we measure a

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February 4, 2020
  • By : srmorgan
  • Quantum Processor Development
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Junction fabrication process

Junction fabrication process is ported to a new oxygen plasma asher. This new tool significantly simplifies the process, improves critical current uniformity, and improves the uniformity of how the junctions age with time.

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