A Quantum Guitar (2509.04526v1)

Abstract: A guitar string represents a wave, and by associating a qubit to each of its playable states we get a quantum wave. This is the principle behind our Quantum Guitar: quantising all strings of a guitar'. In order to achieve this quantisation, we couple a guitar with Moth's Actias quantum synth, and for qubit manipulations including measurements the musician uses foot controllers - hence using all four limbs like a drummer. Our Quantum Guitar also allows for smooth continuous transition fromquantum' to `classical' sound, and vice versa. We have used our Quantum Guitar in several live performances in a variety of venues, playing a number different musical styles, hence demonstrating that it is a very uniquely versatile and reliable instrument. For example, in some performances Quantum Guitar was used in industrial music, by the band Black Tish, who are currently recording an album with it. In other performances Quantum Guitar represented a qubit within a sonified Bell-pair under measurement, the other qubit being mentally realised with a Grand Piano. Classical-quantum and quantum-classical transitions prove particularly useful in musical performance. A link to a demo video of Quantum Guitar is provided.

• The paper introduces the Quantum Guitar, mapping each guitar string state to a qubit to enable real-time quantum modulation.
• It details a hybrid hardware-software system, integrating MIDI pickups and quantum synths for simultaneous classical and quantum sound production.
• The findings demonstrate practical viability in live performance and offer a modular framework for future quantum musical instruments.

Quantum Augmentation of Musical Instruments: The Quantum Guitar

Introduction

The paper "A Quantum Guitar" (2509.04526) presents a comprehensive account of the design, implementation, and performance applications of a quantum-augmented electric guitar. The work is situated within the emerging field of quantum music, which seeks to leverage quantum information processing paradigms for novel musical expression. The Quantum Guitar is constructed by associating a qubit to each playable state of a guitar string, thereby enabling the musician to manipulate quantum states in real time during performance. The instrument is designed to allow seamless transitions between classical and quantum sound, and is engineered for reliability and versatility in live settings.

Conceptual Framework

The central innovation is the quantization of the guitar's strings, mapping each playable state to a qubit. This approach enables the sonification of quantum phenomena, such as superposition and measurement, within a familiar musical context. The Quantum Guitar is not a purely digital or synthesized instrument; rather, it is an augmentation of a traditional electric guitar, preserving all classical playability and sound manipulation techniques. The quantum enhancement is achieved through a combination of hardware (MIDI pickup, foot controllers, sustainer pickup) and software (Moth's Actias quantum synth), with the musician's feet controlling the quantum degrees of freedom, analogous to a drummer's use of all four limbs.

Technical Implementation

Hardware Architecture

• MIDI Pickup (Fishman): Converts guitar string vibrations into MIDI data, ensuring high fidelity in pitch bends, tremolo, and note-off events.
• Sustainer Pickup (Fernandes): Extends the duration of notes, enabling continuous quantum sound. Alternatives include delay and reverb pedals with infinite sustain.
• MIDI Foot Controllers (Boss EV-1-WL): Used for real-time qubit rotations, mapped to quantum gates in the Actias synth.
• MIDI Foot Switch (Boss FS-6): Triggers quantum measurements, implemented in momentary mode for accurate state collapse.
• Volume Pedals (Boss FV500L/H): Independently control the output levels of classical and quantum sound channels.

Software Integration

• Moth's Actias Quantum Synth: Provides a graphical interface for qubit manipulation and sonification. The synth supports arbitrary qubit rotations and measurement operations, with visual feedback corresponding to the quantum state.
• MIDI Routing: The system requires robust MIDI device management, with troubleshooting for device recognition and preset retention. The setup is optimized for use with two laptops, each with dedicated audio interfaces, to ensure reliability in live performance.

Performance Practice

The instrument demands advanced limb coordination, as both hands are occupied with traditional guitar technique while both feet control quantum operations. The musician must be seated to facilitate simultaneous foot control. The architecture supports continuous transitions between classical and quantum sound, allowing for dynamic modulation of the sonic character during performance.

Applications and Performance Contexts

The Quantum Guitar has been deployed in diverse musical settings, including industrial music (notably with the band Black Tish), academic events, and public science festivals. It has been paired with other instruments, such as grand piano and cathedral organ, to realize compositions that explicitly sonify quantum phenomena (e.g., Bell-pair measurement scenarios). The instrument's reliability and expressive range have been validated in high-profile venues, including Wacken Open Air and Merton College Chapel.

Troubleshooting and Recommendations

The paper details practical issues encountered during development and performance, such as compatibility of MIDI pickups with tremolo-equipped guitars, Actias software stability, and device recognition. Recommendations include expanding the set of primitive measurement operations in Actias (e.g., direct X-basis measurement) to enhance playability and reduce reliance on pre-rotation.

Implications and Future Directions

The Quantum Guitar exemplifies a modular approach to quantum augmentation of musical instruments, with the quantum enhancement being entirely hands-free and non-intrusive to classical technique. This architecture is directly transferable to other instruments (violin, wind, percussion), suggesting a generalizable framework for quantum musical expression. The integration of reliable hardware and experimental software demonstrates the feasibility of real-time quantum state manipulation in live artistic contexts.

From a theoretical perspective, the instrument operationalizes quantum information concepts (qubit rotations, measurement, superposition) in a performative setting, providing a tangible interface for public engagement with quantum mechanics. The use of augmented notation (ZX-calculus) further bridges the gap between quantum theory and musical practice.

Conclusion

The Quantum Guitar represents a significant advance in the field of quantum music, achieving real-time, hands-free quantum augmentation of a traditional instrument without compromising classical playability or sound. The architecture is robust, versatile, and extensible to other instruments. The work demonstrates the practical viability of quantum musical instruments in live performance and opens new avenues for research at the intersection of quantum information, sonification, and artistic expression. Future developments may focus on expanding the set of quantum operations available to performers, improving software reliability, and exploring ensemble contexts for quantum-augmented music.