Quantum Analogies for Information Systems – Expert Report
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The Quantum Computing Bottleneck
Human beings create an enormous amount of data in the digital age—from everyday items like social media posts, emails, and searches, to complex information about health, finances, and scientific findings. The International Data Corporation reported that the global datasphere contained 33 zettabytes (33 trillion gigabytes) in 2018, projected to grow to 175 zettabytes by 2025. That’s enough DVDs to circle Earth 222 times.
While quantum computing has been touted as a revolutionary way to intelligently sort through big data, quantum environments are extraordinarily difficult to create and maintain. The fundamental problem is decoherence—entangled quantum bit states (qubits) typically last less than a second before collapsing due to environmental noise. This fragility scales exponentially with the number of qubits, presenting a formidable barrier to practical quantum systems.
Key Limitation: The quantum wavefunction represents a probability amplitude, meaning any disturbance in the quantum system triggers wavefunction collapse. Multi-qubit systems are highly vulnerable to noise, and this vulnerability increases exponentially as the system scales—making large-scale quantum computing extremely challenging.
Classical Nonseparability: Quantum-Like Without Quantum Fragility
Here’s the key insight: while nonlocality is important for specific applications like cryptography, it’s the nonseparability that matters for applications like quantum computing. And particles that are nonseparable in classical Bell states, rather than entangled in a quantum Bell state, are inherently more stable.
In essence, we use sound waves to mimic quantum behavior: for example, creating entangled-like acoustic states (so-called nonseparable states) that behave similarly to entangled particles. In a recent demonstration, our team showed that by stacking and tuning multiple sound waves in an elastic waveguide, we could prepare intricately linked acoustic modes that cannot be separated – an acoustic analog of quantum entanglement.
This breakthrough opened the door to performing “quantum-like” computations with sound waves, addressing the key challenge of decoherence by using classical waves that are inherently more stable. Unlike true quantum systems, these composite phi-bit systems are stable against decoherence and do not suffer from wavefunction collapse upon measurement.
Phi-Bits: The Acoustic Qubit Analogue
A phi-bit (phase-bit) is a classical analogue of a quantum bit supported by a driven acoustic metamaterial constituted of parallel acoustic waveguides. Each phi-bit is a two-level subsystem characterized by two independently measurable phases—the relative phases between waveguides as sound propagates through them.
Hilbert Space Scaling
Multi phi-bit systems are analogous to qubit systems—their representation can be endowed with a tensor product structure scaling exponentially with the number N of bits. A system of N phi-bits spans a 2N dimensional Hilbert space.
Spatial Co-location
Logical phi-bits are defined in the spectral domain, enabling their spatial co-location—they exist within the same physical space. This eliminates any issue of distance in their interactions, unlike distributed quantum systems.
Direct Measurement
Multi phi-bit superpositions of states are directly measurable by contact methods (e.g., transducers) or non-contact methods (e.g., laser ultrasonics)—without causing state collapse.
Decoherence Immunity
Composite phi-bit systems are stable against decoherence and do not suffer from wavefunction collapse upon measurement—the critical advantage over true quantum systems.
Experimental Achievements
16 Acoustic Qubit-Analogue Platform
Our team has experimentally demonstrated classical entanglement (nonseparability) for acoustic logical phi-bits in a 16 phi-bit platform. This provides access to the 216 = 65,536 dimensional Hilbert space, spanning much of its complex nonseparable state volume.
The experimental setup uses an externally driven array of three acoustic waveguides elastically coupled along their length. Each phi-bit is a two-level nonlinear mode of vibration whose state is characterized by a frequency and two independent relative phases between waveguides.
The Sound of Bell States
In a landmark demonstration published in Communications Physics, we experimentally realized acoustic Bell states—the sound wave equivalent of the maximally entangled quantum states that form the foundation of quantum information science. By tuning the complex amplitude coefficients of coupled 1D elastic waveguides, we explored sections of the Bell state Hilbert space, opening new avenues for quantum-analogue computing with phonons.
The Simple Elegance of the Setup
The materials to demonstrate such a complex concept are remarkably simple:
Epoxy to connect them
Rubber bands for elasticity
Standard transducers
Researchers send a wave of sound vibrations down the rods, then monitor two degrees of freedom: what direction the waves move (forward or backward) and how the rods move in relation to one another (whether they’re waving in the same direction and at similar amplitudes). To excite the system into a nonseparable state, we identify a frequency at which these two degrees of freedom become inextricably linked.
Information Encoding and Encryption
Cryptography is crucial in protecting sensitive information in an era when data security and privacy are major concerns. Traditional cryptography techniques, dependent on mathematical algorithms and secret keys, face existential threats from emerging quantum computers.
Our research presents a novel cryptography approach using logical phi-bits. The state of phi-bits displays superpositions similar to quantum bits, with complex amplitudes and phases. The state vector of multiple phi-bit systems lies in a complex exponentially scaling Hilbert space and can be used to encode information or messages with quantum-level security—but without quantum fragility.
We have already accomplished adapting Shor’s Algorithm—an important tool in quantum computing for breaking classical encryption—to use sound waves instead of quantum particles. This could lead to entirely new paradigms for post-quantum cryptography and secure information processing.
Acoustic Transistors and Logic Gates
Bridging Electronics and Phononics for Next-Generation Computing
Borrowing concepts from electronics, acoustic transistors use stimuli (like heating or modulation) to induce a topological phase change that switches sound flow on/off. I simulate and design acoustic logic gates and resonators that could function at radio frequencies. These devices are scalable in size and frequency, meaning designs working at ultrasonic frequencies on the centimeter scale can be miniaturized to sub-millimeter devices at GHz frequencies.
How Topological Protection Works
Topological phononic crystals can manipulate elastic waves that propagate in solids without being backscattered. This is achieved through:
- Valley Hall edge states protected by band topology, observable in both real and momentum space
- Pseudospin polarization enabling one-way propagating bulk waves with immunity to backscattering
- Robust transport across local disorder and around sharp corners without signal loss
Recent research published in Nature Electronics demonstrated the topological valley Hall effect in nanoelectromechanical aluminum nitride membranes at gigahertz frequencies—directly relevant for telecommunications. This work, combining researchers from the University of Pennsylvania, UT Austin, and Beijing University, visualized elastic wave propagation through phononic crystals with extraordinary sensitivity using transmission-mode microwave impedance microscopy.
Revolutionizing RF and Wireless Communications
From 5G to 6G: The Acoustic Future of Telecommunications
The wireless communications industry could benefit enormously from these TA RF devices. We envision a “generational revolution” in wireless tech, where topological acoustic components replace or augment electronic RF filters and antennas. Because acoustic waves can be manipulated with negligible heat dissipation, devices like these promise low-loss, high-Q filters and sensors for 5G/6G networks and Internet of Things (IoT) sensors.
The 5G/6G Challenge
The 7–20 GHz range (Frequency Range 3 or FR3), located between the 5G sub-6 GHz and the mm-wave spectra, provides an excellent trade-off between network capacity and coverage. This yet-to-be-explored range is critical for 5G and 6G applications, but poses significant challenges for conventional acoustic filter technologies. Topological acoustic devices offer a path forward with their inherent robustness to defects and disorder.
Current RF Filter Technologies vs. Topological Acoustics
| Technology | Frequency Range | Key Advantage | Limitation |
|---|---|---|---|
| SAW Filters | Up to ~3 GHz | Low cost, compact | Limited frequency |
| BAW/FBAR Filters | Up to ~6 GHz | Higher Q-factor | Complex fabrication |
| LTCC Filters | Up to ~60 GHz | High frequency | Higher cost, larger size |
| Topological Acoustic | MHz to THz | Defect-immune, tunable | Emerging technology |
Key Application Areas
Tunable RF Front-Ends
Reconfigurable filters, delay lines, and signal processors for software-defined radios. Phase-change materials enable real-time tunability without mechanical components.
Ultrasound Imaging
Medical imaging with enhanced resolution and sensitivity. Topological protection ensures signal integrity through heterogeneous tissue.
Noise Reduction
Acoustic metamaterial barriers that absorb and redirect unwanted sound while remaining thin and lightweight. Applications in automotive, aerospace, and architecture.
Secure Communications
One-way acoustic channels that prevent eavesdropping. Topologically protected signal pathways ensure communication integrity.
Echolocation Systems
Advanced sonar and radar systems with improved range and resolution. Autonomous vehicles, underwater exploration, and aerospace applications.
IoT Sensors
Ultra-low-power acoustic sensors for environmental monitoring, structural health assessment, and smart infrastructure. No batteries required in some configurations.
The NewFoS Vision: A $60 Million Commitment
This research is conducted as part of the New Frontiers of Sound (NewFoS) Science and Technology Center, established with $30 million in NSF funding (with an additional $30 million option over five years). The center brings together nine partner institutions including Caltech, UCLA, Georgia Tech, UC Boulder, and Wayne State University.
Key Output Goal: World-first ambient operation tabletop 50 phi-bit quantum-inspired information processing platform, enabling decoherence-free, measurable, operable, correlated, geometric phase-based massively parallel computing modalities complementary to quantum computing—without quantum fragility.
Looking Forward: The Bright Future of Topological Acoustics
By leveraging quantum-like computing algorithms, it is possible to enable a large degree of parallelism for information processing, which holds the promise for a classical platform based on sound for computation. While parallel efforts have been exploring photonic platforms for these goals, the strong nonlinearities of acoustic waves and the well-established acoustic technology platform offer unique opportunities.
The vision is clear: realize exponentially complex states with a path towards platforms harnessing nonlinear correlations to speed up computational tasks beyond what can be achieved with digital computers—all without the cryogenic cooling, electromagnetic isolation, and extreme fragility of quantum systems.
“Light lasers and single photons are part of the field of photonics, but soundwaves fall under the umbrella of phononics, or the study of phonons. In addition to being stable, classically entangled acoustic waves are easy to interact with and manipulate.”
— Prof. Pierre Deymier, NewFoS Director
Key References
- Hasan, M.A. et al. “The sound of Bell states.” Communications Physics 2, 1–5 (2019)
- Deymier, P.A. et al. “Experimental classical entanglement in a 16 acoustic qubit-analogue.” Scientific Reports (2021)
- Zhang, Q. et al. “Gigahertz topological valley Hall effect in nanoelectromechanical phononic crystals.” Nature Electronics 5, 157 (2022)
- Christensen, J. et al. “A bright future for topological acoustics.” Nature Communications (2025)
Samarjith Biswas 