Chapter: Vulnerability of Quantum Information Systems to Collective Manipulation

TL;DR

This chapter analyzes a previously unexplored vulnerability of future quantum information systems to collective, synchronized manipulation by groups of adversaries who modulate the qubit–boson coupling through a time-dependent profile $\lambda(t)$ in a Dicke-type light–matter setting. Using a generalized Dicke model and the Loschmidt Amplitude ${\cal L}(t)$, the authors show that for $N\ge 3$ a carefully chosen pulse speed $\upsilon^{*}$ can drive the global quantum state to be orthogonal to the initial state, achieving maximal disruption without altering the Hamiltonian or requiring inter-adversary communication. The disruption remains robust to decoherence and scales with $N$, while lone attackers cannot replicate true orthogonality. A practical countermeasure proposed is embedding quantum technologies within redundant classical networks to enable cross-node error correction. The work provides a quantitative framework linking dynamical phase-transition signatures and Loschmidt dynamics to security assessments in large-scale quantum networks.

Abstract

The highly specialist terms `quantum computing' and `quantum information', together with the broader term `quantum technologies', now appear regularly in the mainstream media. While this is undoubtedly highly exciting for physicists and investors alike, a key question for society concerns such systems' vulnerabilities -- and in particular, their vulnerability to collective manipulation. Here we present and discuss a new form of vulnerability in such systems, that we have identified based on detailed many-body quantum mechanical calculations. The impact of this new vulnerability is that groups of adversaries can maximally disrupt these systems' global quantum state which will then jeopardize their quantum functionality. It will be almost impossible to detect these attacks since they do not change the Hamiltonian and the purity remains the same; they do not entail any real-time communication between the attackers; and they can last less than a second. We also argue that there can be an implicit amplification of such attacks because of the statistical character of modern non-state actor groups. A countermeasure could be to embed future quantum technologies within redundant classical networks. We purposely structure the discussion in this chapter so that the first sections are self-contained and can be read by non-specialists.

Figures (6)

• Figure 1: Future quantum technologies.(a) Ultimate quantum technology limit of an extended geographical space covered by a quantum cloud in which the global quantum state is coherent arxiv. This could be a spatially extended cavity of bosonic modes containing an arbitrary number $N$ of qubits (i.e. two-level systems). A group of adversaries attack by applying a pulse interaction $\lambda(t)$ (see Eq. \ref{['hdic']}) between the qubits and a bosonic mode at speed $\upsilon$, with a duration $2/\upsilon$. Our conclusions are insensitive to the precise shape of the pulse, but we show a triangular pulse here for concreteness. (b) An intermediate, simpler version that could be built sooner than (a) because of lower technological demand. It features smaller versions of the $N=3$ qubit-cavity system in (a), which are then interconnected through separate quantum or classical communication channels.
• Figure 2: Disruption caused by an adversary.Top: Complete orthogonality to the initial global quantum state (which in practical terms translates to total disruption and hence maximal possible damage arxiv) is produced by a hostile group (left panel) applying a pulse attack $\lambda(t)$ at pulse speed $\upsilon=\upsilon^*$ simultaneously to $N$ qubits in a bosonic-mode as in Fig. \ref{['fig1']}(a). Since the final global quantum state for $\upsilon=\upsilon^*$ has no overlap with the initial one, the initial state cannot be filtered out from the final one -- hence maximum disruption. This is fundamentally different from an attack by a lone 'Eve' (i.e. single adversary and hence $N=1$) for whom there is no $\upsilon$ that produces the same effect (right panel). The curve in the left panel is for group size $N=3$ but is visually the same for any $N\geq 3$. We use an initial global quantum state of no photons here for simplicity, but our results can be generalized. Bottom: Schematic representation of this disruption.
• Figure 3: Disorder (i.e. entropy) induced by attack. Von Neumann entropy $S_N$, which is a measure of the disorder in the quantum state, shown throughout the attack (i.e. as a function of $\lambda(t)$ and hence starting and ending at $\lambda(t)=0$) for a given pulse speed $\upsilon$ and a given number of qubits $N$. The number of attackers (adversaries) is the same as the number of qubits since each adversary chooses their own qubit. The general case $N\geq 3$ leads to a final global quantum state with maximum entropy when $\upsilon=\upsilon^*$ within numerical error, and hence pulse duration $2/\upsilon^*$. Our numerical calculations suggest that essentially the same result holds for all higher $N$, with the additional impact that the value of the maximum entropy (and hence the disruption) increases with $N$ (i.e. peak becomes increasingly red in the figure).
• Figure 4: Robustness to decoherence. The quantum logarithmic negativity (which can loosely be thought of as reflecting the amount of quantum entanglement) for an open version of our system (vertical axis) as a function of time during the pulse attack, and hence as a function of $\lambda(t)$. The quantum logarithmic negativity has become a widely accepted entanglement measure for an open system and incorporates the effects of natural decoherence and losses from the cavity. Results are shown for adversarial attacks on systems of $N=5$ (solid lines) and $N=11$ (dashed lines) qubits and for several values of decoherence $\kappa$. The results show a surprising robustness against decoherence and losses that increase with the number of qubits $N$ in the quantum information processing system or quantum computer.
• Figure 5: Loschmidt Echo (LE) for a constant pulse $\lambda$. In the realm of deep strong coupling, a sequence of singularity peaks in the Loschmidt Echo becomes apparent, with their emergence dictated by both the coupling parameter $\lambda$ and the time $t$ following the onset of coupling.