The Daily Qubit

🐌 The NSA Uses Internet Explorer and Launch of Letters

Author

Cierra Choucair
April 03, 2024 • Estimated Reading Time: 9 minutes

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Welcome to the Quantum Realm.

I hope you didn’t think I’d dare forget you! Late post this week as I wrap up a project dear to me. The Daily Qubit will continue to be your quick-stop-shop for brief news on quantum computing, but once a week I’ll post to the site a further expansion of a selected research paper delving deeper into the concepts with a little twist. The first issue over today’s Research Spotlight feature can be read here.

Otherwise, enjoy today’s news and send me a message at [email protected] for musings, for fun, for insight if it so appeals to you.

Cheers,

Cierra

QUANTUM PULSE

BRIEF BYTES

RESEARCH SPOTLIGHT

Error-Resilience Phase Transitions in Encoding-Decoding Quantum Circuits

🧪 Tell Me Quickly: This study reveals a phase transition in encoding-decoding quantum circuits from error-protecting to error-vulnerable states, marked by Rényi entropy transitions and multifractality.

🧪 The How:

  • Researchers focused on random quantum circuits composed of three parts: an encoding unitary, a layer for introducing errors, a decoding unitary

  • They focused on coherent errors, in the form of rotations by an angle α, and incoherent errors, represented by local depolarizing channels of the strength λ

  • Demonstration of phase transitions — after being decoded, the logical state of the circuit transitions between an error-protecting phase to an error-vulnerable phase. In the error-protected phase, the decoded logical state is similar to the initial state. In the error-vulnerable phase, the logical state loses its precise information due to incoherent errors. For coherent errors, the original state can be recovered, but only through complex operations across the system.

  • The critical point of the transition is identified and verified through analytical calculations and numerical simulations

🧪 The Why: A comprehensive understanding of what causes a transition from the error-protecting state to the error-vulnerable state can lead to more robust quantum error correction protocols. This study also serves as a peak into the quantum mechanics within many-body quantum systems, which has applications in condensed matter physics as well as statistical mechanics.

QUANTUM LAB

ENTANGLED INSIGHTS

This Week: Representing Noise with Cirq

Quantum computing simulators, such as Google's open-source Cirq, are essential tools for testing algorithms, enhancing the understanding of quantum mechanics, and optimizing quantum circuits without the need for hardware. They are particularly valuable for simulating real-world, noisy conditions that reflect the environmental interference and qubit quality limitations faced by actual quantum systems.

Today, we'll demonstrate simulating phase flipping with Cirq, which indicates an error where the sign of the phase of the qubit has been flipped. These are particularly unwelcome as they don’t affect the probability of finding a qubit in a specific state, but only affect the relative phase which makes them harder to detect.

# Define a line qubit

q0 = cirq.LineQubit(0)
# Create circuit with a 30% chance of the phase of the qubit's state being flipped, measure qubit state and assign to 'results'

#TIP: Vary amount of environmental interaction by adjusting gamma between 0 and 1

circuit = cirq.Circuit(
    cirq.H(q0),
    cirq.phase_flip(p=0.3).on(q0),
    cirq.H(q0),
    cirq.measure(q0, key='results')
)
# Simulate the circuit with reproducibility, execute simulation 500 times

#TIP: Increase number of simulations for a clearer picture of expected results. 100 - 500 might be best for rapid prototyping where computational resources are limited

results = cirq.Simulator(seed=0).run(circuit, repetitions=500)
# Create a histogram with results to see distribution of measurement outcomes

print(results.histogram(key='results'))

More noise representation breakdowns coming this week!

QUANTUM HAPPENINGS

JOBS

Jobs in and around quantum posted within the last 24 hours

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